Thank you for your interest in contributing. As in most open source projects, contributions are very welcome.
Bugs and questions are reported as issues on the github repository. If applicable, try to include a self-contained code example. Also test the latest version (i.e. the "master" branch) in case the issue has already been fixed.
In case this is your first contribution to a project hosted on github you may be helped by this excellent documentation:
You will submit your suggested changes (e.g. new feature/bugfix/documentation/typo-fix) as a pull request. The new version of the code is automatically tested in isolation on CI servers (remember to add your own tests in case you add new funcionality). In addition to the automatic tests, the code will be reviewed with respect to documentation & clarity (docstrings follow the numpy convention and coding style follows PEP8).
If you want to contribute a major feature you may want to discuss this first by opening an issue (in order to avoid unneccessary work in case someone else is already working on something related).