Just go through the issues or try to find your own issue from the project and give it a try.
So after forking the repo you need to make start making change which you want and after done with your changes you can create Pull Request which is reviewed by the owner and if no conflicts found with the exp branch then your PR will be merged.
There are not much of rules not now in order to contribute to this project as this is a beginner level project. So you can go with any format of PR you want but PR must give all the information about what exactly you changed in the code and why.