RIL is like a driver that allows your ROM to communicate with the radio chip on your board. In short... We need it for GSM/HSDPA and our other forms of communications, sort of how your WiFi driver on your PC works.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?