Pretty easy job this one. For small changes to code anyway
From the main repo, create a fork.https://bitbucket.org/hudson/magic-lantern/overview
Give it a name and fork it.
Voila, your own repository.
From there you can browse the source code and edit it.
When you've finished editing the source, it's time to commit it.
You should give it a name that suits the changes you have made.
Once the changes have been committed to your own repo, it's time to create a pull request for merge into the main repo.Note: You can edit more files at this stage before creating the pull request.
You can change the title, add a description, and then create the pull request.Note: You can edit more files (or the same file) at this stage and update the pull request. Just hit the pull request button again and follow the procedure above. A new pull request will not be created, the original pull request will be updated.
And it ends up in the main repo as a pull request
Where hopefully it gets merged into the main source tree.