There are a lot of different ways to contribute. See below for everything you can do and the processes to follow for each contribution method. Note that no matter how you contribute, your participation is governed by our Code of Conduct.
Fork the project, make a change, and send a pull request! Please have a look at our Style Guide before getting to work. Please make sure the unit and functional tests pass before sending a pull request; for more information on how to run tests, keep reading!
Make sure you read and follow the setup instructions in the README first. And note that all participation in the Luca community (including code submissions) is governed by our Code of Conduct. Then, have a look at our running from source doc for more information on how to get set up to run tests and start slinging code.
You will probably also want to have a look at this more in-depth Developer's Overview of the project, how is architected, how to make changes to modules, and so on.
Just use the GitHub issue tracker to submit your bug reports and feature requests. If you are submitting a bug report, please follow the issue template.