Answers for the GitHub Questions

How do you see the files changed within each commit from git log?

To see the files changed in a commit, you would type git log --name-only which will show the names of all the files changed in each commit.

How do you see the contents of what changed within each file from the git log?

To see the files changed in each commit. You would use git log --patch. This will show the difference in each file between to commits.

What does HEAD refer to in the context of git? (Not to be confused with the "HEAD<<<<" one observes within merge conflict)

The HEAD usually refers to the latest commit that has been done in the respiratory.