Stash gives these directions to solve a PR merge conflict
Step 1: Fetch the changes (saving the target branch as FETCH_HEAD).
Step 2: Checkout the source branch and merge in the changes from the target branch. Resolve conflicts.
This is where I'm confused. Is this not affecting the contents of my source branch?. I don't want to merge my target into my source, this can create all kind of problems for me. What am I missing?