Epiar is always in need of help with development, whether from experts or those hoping to learn, we're a community project and at the end of the day, we're all here to have fun: no one is turned away for lack of knowledge.
Specifically, we use the following technologies; you don't have to know them all (or any!): C/C++, Lua, OpenGL, SDL and XML.
The most important thing is to say hello to the other developers - they ultimately will be able to answer questions that this document cannot. To do so, join the epiar-devel mailing list at http://epiar.net/mailinglists and simply post a message stating who you are and what you're interested in.
Explore the Source Code
Download the source code and look around; you might immediately find something you feel is in need of work, but maybe you won't. Talk to the folks on epiar-devel to find out what needs work next, or to find out if your idea is something the team would like to see. The latest source code is available via git at https://github.com/cthielen/Epiar or https://github.com/knowknowledge/Epiar - it does not matter which you pick, both individuals are primary authors.
Submit a Patch
When you're ready to contribute code back, you should submit a pull request to either cthielen or knowknowledge on github.com. If you do not wish to use github, you can always submit a diff'd .patch file but please be sure your code is up to date as of the day you send it.