Is there a tool where I can enter my Lego pieces and it tells me what sets I might have?

Yes! I just did this with 25000 pieces I got on FB market place.
Identifying what you can build: You want: https://rebrickable.com/
Add any sets you have.
Add any parts you have.
Then you can search for what you can build - filtering by exact colours/close matches/any.
You can also filter only official sets, alternative builds for official sets and MOC (make own creation - builds other people have come up with - both paid and free)
Identifying Parts: Finally as someone who took weeks adding all my parts and only discovered this app in the last few days...
https://brickognize.com/
This website you can take a photo of any one piece and it will give you the part number so you don't have to hunt for it on the rebrickable parts list. It is astonishingly accurate!
Other tips: Sort your parts first. I went through 2 key stages...
Reduce to broad categories: brick, plate, bracket, minifigure etc.
remove every part of one type at a time regardless of color and then add them etc.
With rebrickable you can just select 1x2 brick and add 10 black and then just quickly change number and color to 8 green etc. So colour's are not worth sorting til the very end!!
Plus identifying all the green 1x2s in a pile of 1x2s is a LOT easier than identifying all the 1x2 greens in a huge pile of green stuff.
I'll stop now as it's becoming a wall of text but any questions feel free to ask!
- Oh and when searching parts look out for printed parts or very unique looking parts - often you'll find those are in very few sets and it'll give you an idea of sets you might have.
  Additionally rebrickable let's you convert parts into sets if you have all the parts.
- Oooooo boy. Time to go to my parents and get some shit built.
  
  Do it! I cannot stress how much fun it is to discover that your handful of sets can also be built into a dozen other cool things. Especially if you struggle to come up with amazing ideas yourself, the more sets you find you can build, the more you'll learn.
  On that note - if you haven't played with Lego since you were a kid like I did ... you are about to be blown away by how cool some of the build techniques are and what they can accomplish.
- Thank you so much! I guess first I need a nice way to sort all the pieces. I’ll need to look up some advice on that.
  Good thing that I have some vacation coming up.
  
  For me it looked like tupperware city... Every old plastic container I could find.
  This was helpful to me although says much more than needed - for a TLDR just scroll down to the example with the red bricks being categorised into big groups and then broken down again. (I can't emphasize enough though doing things by color is horrendous 😅)
  There isn't anything on here I don't think but I do think there is r/Legostorage (might not have remembered the name perfectly) which has tonnes of good ideas and advice. Ultimately after you have added all the parts you are going to want to store them in a meaningful way to actually get them quickly.

This one might help: https://brickit.app/
Build new creations from your old bricks
Just scatter your bricks and take a photo. Brickit will show you hundreds of ideas for what to build with them, along with the exact location of each piece you’ll need.
I haven't tried it myself, you could give it a try and post what you make?
- Wow. I was joking to my partner last night that these days there should be an app to scan your pieces so you don’t have to enter them all manually. And it seems there is. I’ll look into this, thank you.
  
  This isn't to identify existing sets (unless they added it since I last used it more than a year ago).
  It is more to get random ideas what to build with what it can identify. You are a bit limited since you need to spread out the bricks well enough so it can identify them properly.
  That said, it does work pretty well for that and gave me and my kid a couple nice suggestions what to build.

Rebrickable lets you select the sets you have and tells you what else you can make out of the pieces. Can't recall if you can add individual pieces.

I don't have an answer, just wanted to thank you for the pic! Those old-school pneumatics* (thank you!) gave me a warm, fuzzy feeling!
- I had underestimated how much I had in that box in the basement. I broke it out last night for my 3 year old. It was a bad idea to do that just before bed time ;)
  
  It's never a bad time to Lego!:)) I always get spaceship ideas at 2 AM!:))
  Sounds like a wonderful time, wish you and your wee'un happy bricking!
- hydraulics
  pneumatics :)
  
  Oh, crap, you're right! Sorry and thank you!

Holy shit you have the cool pneumatic bits. Friend had an excavator set that had pneumatic system for operation. It was the coolest Technic set some 30 years ago.
- I remember some sets I had as a kid, and there was definitely a pneumatic one among them that I remember very fondly :)

Some pieces are pretty rare and you can likely search for sets that just include those specific pieces, but it is admittedly hard to quantify what's rare if you don't know Lego.
As an example though, the larger minifigures like you have right in the middle were not common at all, you're looking at maybe 5-6 potential sets at most for that guy. Searching for the more standard minifigures will probably put you on a good path too, parts can be mixed and matched, but the chest pieces will likely be the rarest items. Extra large pieces like the boat piece the person on the side seems to be holding are another good option.

Have you tried using the Lego app ? I don’t know if it will tell you sets but I think it has a feature to suggest builds based on what bricks you have
- I already identified a couple sets I had on brickset.com. The lego builder app doesn’t have the instructions for 2 out of the 3, they are too old it seems.

There are some Sites which do this thing: https://alternativeto.net/software/rebrickable/ .
But sadly they all are properitary and all of them Seem to cost a few dollars for alternative building instructions.

There was an app on ios that recognizes pieces and tells you what you can build. BrickIt i think. Didn't find similar for Android.