hi raam,
a bit more info on svn for you.
http://en.wikipedia.org/wiki/Subversion_(software)
basically the people who are developing openarena use the svn repository to keep up to date with each others work. so it's got newer stuff than is in the latest release. you can download yourself a copy of the svn, build the pk3s and play openarena with all the latest content. you cannot use this content to play online though as your pk3s won't match the ones on the server so they won't let you play.
as well as satisfying curiousity about newer content, you can test the new content and submit bug reports, which can be helpful.
