What platform do you use?
On Linux, GCC is used and all you need to do is type 'make' (assuming you have the required header files). There is a readme file in the source archive that may be helpful.
Setup your files like in the binary distribution (you'll need the asset paks too) and you should be good to go.
I believe the current engine and game source can be found here:
http://openarena.ws/svn/source/081/