You can contribute by creating Pull Requests. (It may take a while to review and merge your code but if it's good it will be merged). Please, implement tests for all your code and use a PEP8 compliant code style. We are using black for formatting so, probably the fastest way to get it right is just running black. All Pull Requests are tested against the latest rocket.chat version. Check that your tests pass and you keep the coverage at least as beautiful as it was before your contribution. Bots and integrations will measure everything for you :-)
Reporting bugs and asking for features is also contributing ;-) Feel free to help us grow by registering issues.
Much more important: Have fun and be nice to each other!