Thanks for your interest in contributing to the Cozo project! As Cozo is just getting started, we aim to keep everything simple.
Contributions to code or other materials should be done via pull requests. You will be automatically prompted to sign a Contributor Agreement (CLA).
As the project matures, ideally before the end of 2023, we will change the CLA requirement to a DCO requirement: see here if you are not familiar with the difference. The reason that we are asking for CLA now is that we want to retain the option to make changes that would become very difficult if copyright is distributed among the contributors, for example if we decide (again) that a different (FOSS) license would suit the project better. If you are uncomfortable with any form of CLA, you can wait until then.
For code contributions other than simple bug fixes, please discuss it first before opening a pull request, otherwise it is unlikely to be accepted.