Every commit (except the first one!) has a parent commit! You can think of your git history as looking like this:

current commit - c6045c - HEAD - “make cats blue”
parent - 304db6 - HEAD^ - “add cats”
grandparent - a92eab - HEAD^^ - “fix typo”
b29aff - “initial commit”

HEAD always refers to the current commit you have checked out, and HEAD^ is its parent. So if you want to go look at the code from the previous commit, you can run

git checkout HEAD^

commits don’t always have 1 parent. Merge commits actually have 2 parents!

git log shows you all the ancestors of the current commit, all the way back to the initial commit