Starting on your newBranch:
git checkout master to get back on the master branch
git pull origin master to get the most up-to-date version of the master branch
git checkout newBranch to get back on your newBranch
git rebase origin/master -i to perform an interactive rebase. The command will take you through and let you pick commits, rename them, squash them, etc. Assuming you will want to keep them all, it will pause when there are merge conflicts and then you’ll have to resolve them in your text editor, it will tell you where (in your text editor) that the conflicts occur. You will have to add those files after fixing them then do git rebase --continue to proceed with the rebase.
When you’re done with the rebase your newBranch will be synced up with master and have any commits in master that weren’t there when you started your work, and all merge conflicts will be resolved so that you can easily merge your newBranch.