[SITUATION 1] You have some changes and John pushes. Now your local Git is one commit behind.

i.e → 1

1. Try git pull to catch up your current branch. If successful, you’re done!
2. If you get Fatal: Not possible to fast-forward, aborting, move on to SITUATION 2.

[SITUATION 2] You already have multiple commits and John pushes. Now your local repo looks like → 1 + 3

1. Use git pull --rebase. Think of this as putting your changes aside, pulling all the pushed changes from GitHub, and then applying your changes on top. This may cause merge conflicts if John changed files that you also changed.
2. If you run into Fatal: Not possible to fast-forward, aborting again, you may have pending changes that you haven’t committed. Try:
   • git stash to stash your changes
   • git pull --rebase to pull John’s commit
   • git stash pop to restore your changes