Trying to understanding the source

Hello guys, I was studying the sourcecode of OpenBSC to get a good understanding of how things work. But due to my lack of experience in Linux programming I have some difficulties to understand the source. I understand that the way bsc_hack works is based on event-queue concept, am I right? Anyway, in select.c I don't understand what's going on when it comes to registering and unregistering fd's in combination with linuxlist.c. Can someone please give me some links where such concepts are being explained, so I can study it? Thanks in advance.