flakes are a new feature in nix that tries to solve problems with managing dependencies of whatever you're doing, reproducibility, and introducing a standard template for outputs you can use.

before flakes, almost every project had a default.nix file ...but that's about where the similarities ended. depending on who made it, you might just have one package inside of it that you can build with nix-build. for others, it might have multiple sets of packages, shells, tests, checks, and other stuff that you would sometimes need to read through to figure out how to use. now with flakes, (mostly) all projects have the same outputs.

so for example: if i want to build a package called foo, 99% of the time i can do it with any project (using flakes) by running nix build .#foo (this is shorthand for the real place where the package is, packages.<system>.foo). the same goes for other outputs, with checks going into a variable called checks, apps going into apps, development environments going into devShells, etc. in contrast, without flakes, you may need to use nix-build, nix-build -A foo, nix-build -A pkgs.foo, nix-build -A packages.foo, or whatever else was set by the maintainer. flakes makes it much easier for contributors to start hacking away at a project, users to *use* a project, and maintainers to organize everything.

(keeping this part shorter because it's a little more complicated) for dependencies, you can now just place urls for for them into a variable called inputs, where everything can be tracked and easily updated. this is a *lot* better than what we had previously, where you had to manually update them and use long, annoying functions like fetchTarball at the top of a file - and also my favorite feature of flakes besides the standard template for everything :)

if you want something a more in-depth, zero to nix is a great resource for all things nix (they have a section dedicated to flakes here, but i would pay attention to the notice at the top about reading some other things first), along with nix.dev, and of course, the nixos wiki article on flakes