Once you have your cnet id and u of c e-mail and all of that, head over to the Regenstein Library, waltz into the privileges office (which is to the left of the barriers you have to walk through to get into the library proper), and pick up your u of c Student ID. Can’t find the privileges office? Just ask, someone will point it out to you.
Once you’ve done that, head over to the Ratner Athletics Center and start pumping iron, swimming, shooting the hoops, or whatever gym/fitnessy thing you like to shoot or pump. Ratner is your gym, and with a Student ID you can just use it, no fuss no muss. Speaking as someone who didn’t do a whole lot of pumping during my MAPH year, staying fit can really help you stay sane.