git status and git diff explained
git status lists which files are modified, staged or new, and whether your branch is ahead of or behind GitHub. git diff shows the exact lines you changed: - for removed, + for added.
Step by step
What changed?
$ git statusWhich lines, exactly (not yet staged)?
$ git diffWhat will the next commit contain?
$ git diff --staged
Neither command changes anything, so run them as often as you like. Most git confusion goes away by running git status first.