When your drupal branch is ready for merging you'll have to put it in a public place so that other people can get it. Publically exposing one of your branches involves "pushing the branch". One can push a branch via sftp or rsync if BzrTools is installed.
One pushes a branch in the following manager:
$ cd my-drupal-fix
$ bzr push sftp://hostname.com/public_html/my-drupal-fix
Once you have pushed your branch you'll want other people to know about it so that they can merge you. You can do this by registering your branch on Drupal Launchpad page. New branches should be marked as "NEW".
The person responsible for merging Drupal branches will merge your code in the same way that you merge Drupal code. He or she will then review your code and will email you. Two possible reactions are likely: either your hacks were accepted and merged, or your hacks need some more work. Don't get discouraged if you need to do more work; just fix the outstanding problems, commit, push again and ask that your branch is reviewed.
*NOTE* There is currently no person responsible for merging. Please see the next chapter about generating a diff.