Plopping down works. Hang out in a common area in your dorm. Do some of your reading outdoors (don't plan on getting much serious work done). Get to class 15 minutes early. Go to parties or clubs that look interesting. There will be someplace where different groups have tables at the start of the year; wander down there and talk to the people at the tables.
You're going to be in an environment in which (a) a lot of other people are in exactly the same position as you, and (b) still other people are trying to recruit members of the first group to do whatever it is that they do.
If your mom takes you, try to prevent her from giving your address and phone number to a cult because she doesn't think you can make friends on your own. Wait, that probably isn't a worry for most people.
(In fairness, the cult members were very nice. I just didn't want what they were offering.)