ELI5: How can my school tell if I'm downloading something illegally and what can I do to prevent them from catching me?

The title says it all. If it matters at all, the school is Indiana University in Bloomington, IN. I guess what I'm asking is, how do they track people torrenting things and what countermeasures can I take to mask myself from their search? I've heard tale of a girl who "hacked" (not sure if appropriate word) the school's something or other and registered her computer as a printer, so they can't tell that she's downloading things, but a) I'm not sure of the validity of this and b) as you can tell by my technological jargon, I have no idea how to go about doing that. So, please and thank you for your assistance, Reddit :)

Also, this being Reddit, I'm sure this goes without saying, but the illegality of my actions are not a huge concern to me.