First of all, thank you for taking the time to contribute to this project.
Contributing to a project on Github or Gitlab is pretty straight forward. If this is you're first time, these are the steps you should take.
Fork this repo.
And that's it! Read the code available and change the part you don't like! You're change should not break the existing code and should pass the tests.
If you're adding a new functionality, start from the branch master. It would be a better practice to create a new branch and work in there.
When you're done, submit a pull request and for one of the maintainers to check it out. We would let you know if there is any problem or any changes that should be considered.