Subsystems

After you feel you understand of the architecture of the system and have the source code built and running, you'll want to jump into a specific area and start contributing. At this stage its helpful to understand the directory layout of the repository:

build/ - CMake build system, will need to be updated with any new projects or source files
cppoh/ - C++ ObjectHost binary, what you'll run to simulate objects (which are "scripted" using C++, eventually we'd like other object hosts too)
externals/ - external projects that are hard linked into our tree
libcore/ - Core library, mostly utility code that will be used all over the system, including in the ObjectHost and Space. 
liboh/ - ObjectHost library, contains interfaces and some code which is shared among all ObjectHost implementations
libproximity/ - Proximity library, shared interfaces and implementations of proximity related services
libproxyobject/ - Code for objects -- interfaces for persistence, graphics, communication -- and proxy object management.  (Should be libobject or similar).
libspace/ - Space library, contains interfaces and some code which is shared among all Space implementations
proximity/ - Proximity binary, what you'll actually run to run a proximity service, uses libproximity, adds implementations, plugins
space/ - Space binary, what you'll actually run to run a space service, uses libspace, adds implementations, plugins

Based on the above listing you'll want to dig deeper into whichever directory contains the area you're interested in working on.