For the latter, most large games use an asset management system. Either homebrew, or something like Alienbrain. (Well, people used Alienbrain when I left. Not sure what's hip these days)
For in-game, there's usually a fairly strict organizational scheme. It depends on the game, but usually folders are about "location" - which map, which part of the world, which episode, etc. Asset names indicate a name, and various other bits like left/right hand hold, color, or whatever matters for that asset.
It's usually the lead artists job to come up with said scheme, unless you have a tech lead for the asset pipeline.
If you look for assets, you do a search in the asset management system, which also contains the in-game name and location.
For smaller games, you make do by manually organizing, but as things grow, you'll start hand-rolling tools.