Contribute to Rocket.Chat FAQs
Beginners are strongly recommended to start with the issues having "good first issues" labels. They can also try their hands at contributing to documentation and raising issues (after all these are also different types of open source contributions).
If you are stuck with anything in the codebase, please contact the vast community of growing programmers in Rocket.Chat. You can also take help from Rocket.Chat forums. Just tag the person you think will be able to help you best according to their respective fields of expertise and tell him/her about your issue, and they will be more than happy to help you out.