my experience of mentoring was positive but just sign up and see if you like it, if you dont, then as already mentioned, you dont have to keep going
the idea of peer mentoring is to help students settle into uni. social events are held with the idea that 1st years can meet eachother outside of lectures and have some fun too. you are also given a mentor who will be able to answer those questions you have about uni but dont know who to ask about them