why do you want to skip it?
freshers week refers to the actual social events of the first week (occasionally two weeks at some unis) of university - so the first week after you move into your halls
most of these will be drinking activities which I'm assuming is the issue... most universities now have SOME sober events as they are more aware that drinking only stuff can cause people to feel lonely and drop out - but it may be a little harder to find the sober events... my university did things like roller disco, BBQ etc so it was popular stuff that plenty of people went to
skipping social events won't ever affect your academic marks (except perhaps to improve them if you arne't hungover in your lectures) but, particularly in the first week, it's important to go along to a few things to meet people or university will be very lonely and the atmosphere in your halls might not be nice... you don't have to drink or stay super late but show up for a few hours on a few nights so you know everyone
EDIT: sorry just seen you're a mature student and commuting in - in which case ignore the above... go to your lectures (ALL of them) as they will tell you important course related things, you can meet people and it generally leaves a bad impression on lecturers yo may want help from later if you don't turn up... skip the drinks and parties if you want to that's no big deal, perhaps try and find a couple of people on your course on FB so you have someone to sit with on the first day? I did this and met that person to go to the lecture together which was nice