How I can add some contrib to bzr main-line?

First, join the development mailing-list; that's where new contributions are reviewed and decided upon. There are two ways of getting attention to your contribution:

If it's a small patch, then develop against the main trunk and when you are satisfied, use "bzr send" to email a bundle to the development mailing-list. There, the diff will be visually inspected and perhaps applied to a tester's tree.

If it's a significant contribution that is larger than someone can easily review in email, then you should use Bazaar to publish a branch. Then, inform the development mailing-list of your new branch and give a summary of what it does. They may download and inspect the changes.

In both cases, if the contribution is accepted, it will be merged to the main branch within two weeks or so. Often, contributions need more work (as for instance, you forgot to add tests to prove correctness), and you'll be invited to improve your contribution and try again.