LAN header programming question

someone explain the protocol for this LAN: header you have and how
private networks work with this, what are typical
set ups? does everyone just plug into a ethernet plug (what type) built into every dorm wall, turn on their
computer and do a dhcp from some central server
or do they have to be assigned a ip from
some admin thing? who decides what server
gets to be a dhcp, and can they just turn you off
if you use too much bandwidth? any ways around this?
do you have to log into some sort of proxy? how does that work? can I come there and plug in as a guest? library access? wireless?
details, details, thanks! (links?)