A little bit of backstory. Me and a few friends from my job decided to play D&D 5e while we we're kinda stuck at in one place and were quite bored. So we got everything we needed and they chose me to DM. None of us ever really played but we got the hang of the rules rather quickly after a few sessions.

Now my problem is that my group focuses too much on like, extreme details and search every little corner of every room I present them. For example they arrive at a ruined village that was destroyed several hundreds of years ago and got plundered and emptied over the years. The ruin itself had no connection to the Quest they were given, it was just a ruins I put in front of them while they traveled to another location, nature took over so they had to deal with giant spiders etc.
Anyway, they searched every little corner of every single building. They wanted an entire layout of the village so they could look through every single house. But then they got pissed when I had to tell them 90% of the time that there was nothing left since the village was raided, so useful and precious things were all long gone. They kept going tho and as I mentioned, got really pissed about it (plus they had some really bad luck when it came to dice rolls during combat).

That's just one example, there are many more where they are just too focused on small details I'd never think would even matter. Like the eye colour of a farmer who was around at the market, search every single pocket of a slain enemy or wanting to know the name of EVERY book in a bookshelf to know if it might be useful or whatnot.

I'm afraid that if I tell them to stop doing that, they might end up ignoring details or hints I throw at them, blindly running through the world. Don't get me wrong, I like that they are invested in everything I present them but it is just extremely tiring for me as DM and things like "Searching a ruined building" take an unnecessary long amount of time.

Since I don't have experience as a DM , I don't know if it's just me being dumb and furthermore I don't know what to do so I'd really appreciate some advice.

How do I keep my players from focusing too deeply on unimportant details, without causing them to miss important ones?

First, no, you're not being dumb. I'm not sure exactly how common this sort of problem is, but it's definitely not uncommon. I've seen it before. Especially as video games get more and more detailed by procedural generation (or just massive amounts of back-stage effort from a paid team), players sometimes expect unreasonable levels of detail. And honestly, sometimes before the rise of video games.

Second, sometimes, for some of these things (eye color is a specific example because you mentioned it) it's actually not hard to just wing it and come up with meaningless details on the fly... precisely because they are meaningless. It's a good skill to have, within reason. But yes, it can and does get tedious, especially if they're expecting you to remember all this stuff many sessions later, or are reading deep significance into it.

Third, the easiest solution to this is probably to tell your players (politely, kindly) something like, "Hey, guys. This is putting a heavy burden on me that isn't fun and isn't really meaningful for the game. I'm not running a game where your failure to search every stick of furniture in every ruined dwelling place is going to make or break the success of your quest. It's really hard to be coming up with bookshelves full of book names when none of them are actually important. Can we maybe... ease off a little and find a happy medium?" Not those words, but that sentiment. Be willing to express an idea of where that happy medium should be, by the way.

Fourth, and very specific to the 'search every stick' mentality: As the GM, you are not merely allowed to set the scope of a single search roll, it is a vital tool in your toolbox to control the pacing. What I mean is this:

Sometimes, it is appropriate to bring out a grid mat and track character motions very carefully, turn by turn, and 5' resolution. Almost always, this will be in combat, when it is important. But most of the time, especially when just getting from here to there across town or across country, it would be foolish and infuriating to do that.

By the same token, sometimes it is appropriate to search something room by room, or even at a finer resolution-- in some kinds of dungeon crawls. In many other circumstances, you can and should say, "Okay, I will make a search roll for you for the entire ruined village. Or (or in addition to that) you can also turn things back on them a little bit: "What specifically are you looking for? I will tell you if you find any in that ruined village."

These are tools that let you control the pacing of the game, and that is definitely something within your sphere as a GM.

Some advice that might help:

• Have a chat with your group, and explain to them, politely, that details like the name of every book on a bookshelf are inconsequential and slows down the game.

Tell them that if they want to try and find an interesting book on a bookshelf, they should tell you what kind of book they're looking for ('Is there a book about old legends?'), then you as a GM decide if it's logical to find it on this bookshelf, they're unlikely to find anything about old legends on the bookshelf of the city's treasury for example. Then you can either have them make a roll to see if they notice anything interesting, or just tell them if there's something of interest or not.

• About wanting to search the ruined village or every pocket of an enemy, that is natural player reaction: the GM put something in front of us, there might be something interesting in there. Plus looting an enemy is normal for D&D and many other games. That's easily solved with one roll of dice, and some RP, as well.

If they want to search the entire ruined village, tell them it will take them hours and they may be late for whatever they have to do, if your current adventure has a time sensitive element, for example.

If it does not, or they want to do it anyway, have them make one roll and describe to them that, after a long day of trudging through the ruins, in the dirt and such, almost falling through rotten wooden floors into cellars or narrowly avoiding getting crushed by falling stones from the walls and such, they find nothing. And now the night is almost upon them, they are exhausted and dirty, time to set up camp.

Same with looking through an enemy's pocket: have them make one roll and describe what they find depending on their success and keep going.

On both cases, the roll and description took two minutes, and the adventure can continue.

If a player complain, you can just point at their roll and say: 'That's what you find with this result.'

Note about the layouts and maps: The only time I do a layout or a map is for combat. It is especially important in D&D, but even in other games, I usually do not have maps of cities and such ready, except for combat to help visualize. Or, if my players are really lost my description, I whip up something quickly based on how I envisioned the place in my mind.

I've run sci-fi games where the players go to different planets, and just gave them a quick verbal description of the planet. There is an agreement with my players that making layouts takes a lot of time to make, and that, while they're nice, it's often time wasted if the layout will be used only once in a scene in passing. You can explain this to your players as well, they should understand. If they don't, you may have a bigger problem than you realized.

• For NPCs, have a gallery of them ready and make your description from the start, giving them the details like eye color.

I find that that kind of details adds to the NPCs, give them a better presence than just saying 'you meet a farmer that looks like a farmer'. I'm exaggerating with that description, but you see my point. Even if you reuse them, having a premade gallery of NPCs help you to give a credible description of someone they meet, and this participate to give the world more depth and realism.

Set their expectations on what you can and cannot do straight.

I remember the same thing from my first D&D session. We were walking along, chatting amongst ourselves, when we came across a cow. Since that was one of the first things we, as players, encountered in that world, we bombarded the cow with skill checks and wasted like 15 minutes. In the end, it was just a regular goddamn cow (who would have guessed ^^).

Ultimately, we learned from this encounter (and various others in the first few sessions) that not everything is mysterious just because the DM mentioned it.

Where is your players' behavior coming from?

Concerning your players: The first thing we need to figure out is why they focus so much on details. Is it like in the example above, that they simply think that because you mentioned it, it has to be important? Or is it something else?

The way I see it, however, is two-fold. On one hand, I'm gonna go out on a limb here and say that your players came to pen & paper from video games (or behave like someone who does), and as a consequence, they have unrealistic expectations on what you can and cannot do.

Your players are behaving like they are used to behave in video games.

First of all, your players seem to be highly focused on looting, indicated by the fact that they're pissed when they want to loot the ruin but there's nothing there. This is directly related to their (supposed) video gaming background I mentioned above.

More precisely, video games run on high-performing computers, which have no issues whatsoever in tracking every little piece of trash that the player picks up.

Coming up with (as DM) and tracking (as players) this kind of loot is, however, not viable in RPGs. Additionally, making each of your players roll 15 separate investigation checks for every single ruined house, giving them a broken broom (metaphorically or literally) on a "success" is not fun for anyone. Instead, if they want to loot the ruins, summarize it as

You search the ruins, noticing in the process that they were abandoned centuries ago. Suspecting that you're probably not the first raiders, you attempt to find anything worthwhile left behind. Make an investigation check.

Depending on how roll-loving your group is, you can make everyone roll, or let one person roll with advantage. The latter would mechanically be the Help action, meaning that your most investigative player checks out the place and gets help from the others.

I suggest using the latter version since the first version means that regardless of the DC (unless it's higher than 20, ruling out players with low modifiers), there will likely always be at least one player succeeding on the check. This is less problematic during looting since you can simply scale the loot based on the number of successes, but it will get problematic during boolean checks - i.e., how can I activate this extendable bridge? In that case, only one person has to succeed.

Insisting on the first version would be rather cheesy from your players, but which one you agree on (or which one you choose, since it's ultimately your decision) depends on you and your group.

As a consequence of treating D&D like a video game, your players have unrealistic expectations of you. Make it clear to them that you're not a computer.

The second problem that your group seems to have, which in my experience is not uncommon either, is that they have unrealistic expectations of what the DM can and cannot do.

For example, when your party ventures into a new town, you as the DM can prepare a few NPCs, such as a major, a vendor on the marketplace, and a cleric in a local temple.

Furthermore, when your players suddenly decide to search for a rather exotic kind of NPC, such as an herbalist or a cobbler that you didn't prepare, you should be able to come up with one on the spot, using things like name lists that allow you quickly improve the NPC. (This can be rather hard to do in the beginning, don't get discouraged - it gets easier.)

What you cannot do is to prepare a list of 200 books that a bookstore you potentially just improvised sells. Your players, being accustomed to video games which require years of development (unlike your session), want to look through all of the books to make sure whether or not there's a book that they might like or could use.

You need to make it clear to your players that this kind of preparation would require an enormous amount of preparation that simply exceeds all realistic expectations. This is a key argument, if you can't get your players to accept that there are limits to what you can do and prepare for, it won't work out.

It might help to let other people be the DM in a oneshot, so they realize what they're asking for, but I feel like that would just create other problems down the road (e.g. players trying to tell you that you're doing your job wrong, since they know a little bit about it as well). Hence, I would only choose this means as a last resort.

To handle a situation where players want to look through a bunch of books, make it clear that what they want to do is what their characters are doing, but you only present them with the conclusion that their characters came to. Similarly, your players probably don't roleplay going to the toilet (or even mention it), even though your characters most certainly do use the toilet.

You can describe it as following:

Your characters casually walk through the bookstore, letting their eyes wander over the rows of books. Occasionally, one of the books catches one of your characters eyes, but mostly, it turns out irrelevant after all. They ultimately discover 3 promising books: A treatise on the anatomy of Beholders, A complete history of the town of Thunderhall and Dissecting a wyvern: cooking recipies and a guide to poison extraction.

Obviously, you can switch out these books for something more suitable for your campaign. It might also help to have a number of book titles prepared (I'm sure you'll find a bunch on google), so you don't have to come up with them on the spot.

I also recommend you to check out How can I handle players who want to browse shops at random? (disclaimer: I originally asked & answered that question).