If you try to git commit and don’t specify -m for a message, or if you git pull and there’s a non-fast-forward merge, or if you git merge and there’s a non-fast-forward merge and you don’t specify -m, or what I’m sure are a host of other reasons, you might get popped into an editor.
And you might not be familiar with that editor.
So here’s how to get out of it.
Nano: If the editor says “Nano” or “Pico” in the upper left, then edit the commit message (if you want), then then hit CTRL-X, and then hit Y to save, then ENTER to accept the given filename.
Vim: If the screen has a bunch of ~ characters down the left and a crazy-looking file name at the bottom maybe with the word All, you’re in Vim or some other vi (“vee eye”) variant. Press i, then type a message (if you want), then hit the ESC key in the upper left, then type two capital Zs in a row. ZZ. That should save and exit. Learning Vim57 is beyond the scope of this guide, but this author thinks it’s worth it for the editing speed you can achieve.