If you're interested in contributing to ShinyCMS ... let me start by saying "Thank you!" :)
If you already know what feature or fix you want to work on, then it's the usual process; fork the repo, do your thing, submit a PR when you have your new code working. Please make sure it has full test coverage.
If you're generally interested in getting involved, but don't have a specific task in mind, here are some things to read that you might find useful:
You might want to start by looking at the issues tagged 'good first issue'; they're the ones that I think are particularly unlikely to turn into a nasty complicated mess halfway through. :)
If you find something that you'd like to tackle, but you're not feeling entirely confident about it, please do get in touch with me. I'd love to help you if I can, whether that's by talking the problem through in more detail to make sure you feel like you understand it, or discussing possible solutions, or even pair-coding with you on the solution you (or we) decide to try - whatever you think is most likely to help you, both with the issue at hand, and more generally as a software developer.
When I first started contributing to open source projects, I received a lot of incredibly valuable help and advice from more experienced developers - I would welcome more chances to pay that forward.
This project has a Code of Conduct, which is intended to make using ShinyCMS, or contributing to it, a harassment-free experience for everybody involved - regardless of who they are and what they do or don't know.
Please read and follow the code of conduct - thank you.