Git: View History/Log
How to get a history of commits?
show last 3 commits
git log -3

This command is important because it shows the ID for each commit. You'll need to use the ID when doing comparisons or diff or revert.
[see Git: Diff Between {Working Dir, Staged Area, Last Commit}]
[see Git: Revert Change]
How to see last change?
# show diff of last changes git log -p -2 --color

git help log