title: What are staged/unstage files in SourceTree (with Github) and can I pull files selectively?
body: <p>I have a project with a notification like "develop 10↓". Does this mean there are 10 files changed recently on GITHUB since the last pull?
  Where can I view the files that were changed? Can I pull them selectively? (only a few of them after revising each). 
  Where can I review the before-after differences? 
  What is a staged/unstaged file? Any good and straightforward tutorials, please let me know.</p>