Your branch is ahead of ‘origin/master’ by 3 commits

I am getting the following when running git status

Your branch is ahead of 'origin/master' by 3 commits.

I have read on some other post the way to fix this is run git pull --rebase but what exactly is rebase, will I lose data or is this simple way to sync with master?

You get that message because you made changes in your local master and you didn’t push them to remote. You have several ways to “solve” it and it normally depends on how your workflow looks like:

• In a good workflow your remote copy of master should be the good one while your local copy of master is just a copy of the one in remote. Using this workflow you’ll never get this message again.
• If you work in another way and your local changes should be pushed
  then just git push origin assuming origin is your remote
• If your local changes are bad then just remove them or reset your
  local master to the state on remote git reset --hard origin/master