configuration.nix by Example
Your configuration.nix is a module. It defines some of the options declared in
modules elsewhere, usually for the most part ones in
<nixpkgs/nixos/modules>.
You can search for information about these options on this
page.
When you alter your configuration, you can type nixos-rebuild switch to switch
to it and make it the new default. You can also check the NixOS
Commands page for different ways to use
nixos-rebuild.
What follows are some example configurations to hopefully give you some helpful context for how NixOS modules are configured.