GIT - How to Backtrack in Git

Reference : Codecademy - Learn Git - How to Backtrack in Git

• git checkout HEAD filename : Discards changes in the working directory.
• git reset HEAD filename : Unstages file changes in the staging area.
• git reset commit_SHA : Resets to a previous commit in your commit history.
• Adding multiple files to the staging area with a single command:

  git add filename_1 filename_2