How do you merge branches?
If you want to merge a branch (e.g. master to release), make sure your current branch is the target branch you'd like to merge into (use git branch or git status to see your current branch).
Then use
git merge master
(where master is the name of the branch you want to merge with the current branch).
If there are any conflicts, you can use
git diff
to see pending conflicts you have to resolve.