The following is a basic and incomplete list of operations, which are illustrated below.
git pull
Fetches remote changes into the local clone, and merges them into the current working files.
git checkout
Replaces the current working files with files from a branch.
git checkout --track
Creates a local branch from a remote branch, links them, and replaces the current working files with files from that branch.
git fetch
Downloads changes from a remote repository into the local clone
git reset
Makes the current branch point to some specific revision or branch.
git reset --hard
Makes the current branch point to some specific revision or branch, and replaces the current working files with the files from that branch.
git merge
Merges files from a given branch into the current branch.
git push
Uploads changes from local branches to the respective remote repositories.
git add
Puts current working files into the stage (aka index or cache)
git commit
Commits staged changes to a local branch
git commit -a
Commits all modified files to a local branch (shorthand for "git add" and "git commit")