Git: beyond the basics

When you first learned git

Remember your first programming class where you had to use git to turn your work?

You set it up the first day of class and only really had to memorize commiting and pushing.
You used it after you were done with an assignment, not as a part of your workflow.
You were taught how, but probably not why.

What you probably already know

You vaguely remember,

git clone
git init and git remote add

You know,

git add and git commit, or the potentially sinful git commit -am
git push

and maybe you've seen or heard tell of,

git log
git checkout
git branch
git merge
git rebase