TaskChampion sync-server is very open to contributions, and we'd love to have your help!
A good starting point might be one of the issues tagged with "good first issue".
This repository is a typical Rust application.
To work on it, you'll need to install a recent version of Rust (the latest stable is always a good choice).
Once you've done that, run cargo build at the top level of this repository to build the binary.
Alternately, run cargo test to run the test suite.
We expect contributors to follow the GitHub Flow. Aside from that, we have no particular requirements on pull requests. Make your patch, double-check that it's complete (tests? docs? documentation comments?), and make a new pull request.