Feel free to put up a pull request to fix a bug or maybe add a feature. I will give it a code review and make sure that it does not break backwards compatibility. If contribution is in line with the vision of the project, I will work with you to get the code into a mergeable state and merge it into the master branch. If you have contributed something significant to the project, I will most likely add you as a collaborator given the ability to merge others pull requests.
It is very important that new code does not break existing code, so be careful about what code you do choose to merge.