First of all, thanks for dedicating your time on this project, your contributions are very welcome.
Feel free to navigate on the code, run code analysis tools etc, to spot bugs or vulnerabilities.
You can check the issues to find something already mapped out, if you find a new issue you can add it, suggestions are welcome too!
After finding an issue to work on, fork the repo, make the desired changes. Then use shellcheck to lint the code, please fix any warnings before submitting your changes.
Now you can submit the PR. I'll review it and if I'm happy with it, the PR will be approved and merged.
And that's it, you made a contribution.