Saving in Git is two steps, not one. First you stage what you want included, then you commit the staged set as a snapshot.
git add <file> moves a file into the staging area (Git's "draft tray"). You can stage several files, then commit them together as one logical change.
git commit -m "msg" writes the snapshot. Once committed, that snapshot has a unique ID and is permanent — even if you edit the file again, the old version is recoverable.
Why the two-step? Because real commits rarely match "everything I've changed." Staging lets you commit the bug fix without the half-finished experiment sitting next to it. Good messages use the imperative mood ("add login", not "added login") and explain why.