If you are interested in contributing to the project here are some ways to contribute
Help track down and fix bugs. Reporting issues to the Issue Tracker is probably one of the easiest ways to make a contribution. Bugs cant be fixed if they are not found. Another way to contribute is volunteering to fix bugs listed on the tracker and submitting patches (Making Patches).
The unit test suite could greatly benefit from more extensive tests and tests for more objects and functions in Editra's api. Editra's unit tests can be found by doing an svn checkout of the source code and looking in the Editra/tests/, all the tests use the standard Python unittest framework. Writing unit tests is a great way to become acquainted with the api's available in Editra.
Need some extra functionality from Editra? Writing a plugin is another fairly easy way to contribute an enhancement to the editor. If your developing a plugin and having a substantial start on it, let me know and I can provide source control over at Editra Plugins as well as support for additional internal api's and management of interface translations.
If there is some feature that you believe belongs in Editra proper and think you can implement it, please start a discussion about adding it in advance. Discussion through the community page, or mailing list are the preferred places to start. Also see the Coding Guidelines before starting to write any code that will be included in the Editra core code.
Don't think you can contribute in any of the other ways listed above. Making a donation is another way to contribute by helping to cover the server fees and development costs.