To create a new branch in GitHub Desktop, first click the header on the right that says Fetch origin. If GitHub Desktop finds new commits on your remote repo after clicking the header, the text will change to say Pull origin and will display the number of commits to pull. Click Pull origin to merge the commits into your local branch.
Using the Pull origin action may cause merge conflicts in your local repository. Make sure you resolve the merge conflicts before moving on.
If you have local commits that haven’t been pushed up to your remote repo yet, the header on the right will say Push origin rather than Fetch origin. If you’re ready, click Push origin to push your commits and reset the header text back to Fetch origin.