Everyone moves in at the start of it and then for the rest of the week there are lots of registration sessions for various things, also introductory sessions for your subjects.
Apart from that it's just about having fun! At Aston freshers week has a theme so superheros etc. We had daytime things like taster sessions for the different clubs and societies, trips to Alton Towers/Cadbury World and then loads of different night time events too.
Then at the end of the week we had Freshers' Fair which is where you join up to any clubs/societies that you want to & get lots of freebies!