What's up Na5! The PIN, is how the RIM server identifies your BlackBerry, it's sorta like an address, or like an IP address (if you know internet at all) that tells RIM what device is connecting to it's server, or to another BB. With a PIN you can send messages directly to another BB called a PIN messages (these are free text messages), and also you can use RIM's special IM client called BBM, or BlackBerry Messager, which is similar to AOL Instant Messanger, or Yahoo Messanger, BUT it's JUST for BB users. The PIN is MUCH MUCH more to RIM thou, here is a wiki page that explains how it all works....
