Hi and welcome! You have a steep learning curve ahead of you, but all help is greatly appreciated! Its mostly C++, but PHP, Python and SQL will be very helpful as well. Ruby is used a bit, too.
The first thing to understand is the DCE system. This is a communications protocol (using TCP). Most of the LMCE system is modular using "DCE Devices" These are software modules that communicate with one another through the DCE protocol - it is an abstract command and data protocol for doing things like "volume up", "on/off", "turn light on", "play piece of media", etc. Each DCE Device is responsible for interpreting what that means in its context should it receive one of those commands. This way someone can add an entirely new DCE device to the system and the system does not need to understand how it does stuff, it just has to issue the appropriate abstract command and the device handles its interpretation.
Devices can be existing applications/packages/software that just have a DCE "wrapper" around them that translate the DCE commands into whatever control system the existing package has, or can be written from the ground up - using C++ LMCE provides some tools like DCEGen that give you a jump start.... this creates a skeleton/stubb piece of code with methods for all the DCE commands that you want to implement, and then you just drop the necessary code into those methods.
All DCE devices communicate through the DCE Router which sits on the LMCE core. A DCE device can be on the core, next to the DCE Router, on an MD (Media Director) over the network or anywhere else that is addressable on the network. Current DCE Devices can be viewed in the Web Admin under the Devices Tree. It is a hierarchy of devices, however not every object in that tree is a DCE device - some are just representative of functional units within a LMCE environment, and usually the "parent" device is the actual DCE device that sends/receives DCE commands on behalf of the child device.
The telecom subsystem is based on Asterisk and a DCE wrapper was written to interface it with the DCE system; whereas the media subsystem primarily uses xine-lib - the libraries that Xine also uses, and some DCE code was written to create a native DCE player from the ground up using those libraries.
I would advise you do lots of research on LMCE and DCE and how the infrastructure works. Then look into how you set up a Dev environment and collaborate with the other Devs through the CVS system.