What does the android source contain?

I'm currently downloading the android source code, because I want to try and install it on an older mobile device. Now when I buy a mobile, of course, there are lots of apps preinstalled, wcich are of course not included in the source. But I wonder what exactly is included. Is there somewhere a list to see what is in there? Or is this only the kernel and a core operating system and nothing else?

For example, if I format the device, and install the self compiled android, do I have to get the device specific system drivers from somwhere else (which I assume). Is there some kind of tutorial on how to build a working android device from ground up to the point where I can use it for telephony?