So you've decided to contribute to VoxelPlanet? Splended, we're always happy to accept contributions!
We take two types of issues: bugs and feature requests, as do most projects. If you know how to code in C++ or another language used in the project, we also take pull requests. We recommend pull requests over issues, for two reasons: 1) making a pull request can ensure speedy implementation of the desired feature, since you already added it to the program, and all we have to do is merge it; otherwise we might forget about it. 2) If one of your pull requests gets merged, your name will be listed on the project as a contributor! However, if you aren't sure whether we'd accept your pull request, you can still create an issue to make sure we'd merge your pull request before you start working on it.
So yeah, have fun!