In the menu bar, select
Packages -> Package Generator -> Generate Atom Package. Give it a name, like
dayogreats' Snippets. Then go into the folder (you can do this in Atom, in your file manager, or in the command line), create a folder entitled
snippets, and make your files inside it. You might end up with a file tree that looks like this:
Naming the files with the language first will allow you to sort them alphabetically easily find the one you want.
Now, open the command line interface for your system and navigate to
apm link and Atom will create a symbolic link in
.atom/packages that points at your package, so Atom will load your package as if you had installed it.