Milan is served by a very good public transportation managed by ATM. There is a very good subway net, with three lines crossing the whole city and a good amount of buses and trams, which will get you almost anywhere you want. The price for one ticket in the city area is € 1,5 and it is valid for one trip or 75 min's. There are also a 24h ticket and a "carnet" which is ten tickets for a lower price.
But you are probably more interested in a monthly or even yearly card. The good news are that there are both and they are pretty cheap for students. The monthly ticket costs € 23 every month, plus € 10 the first time for the card and a picture. To get your card, you have to go to one of these offices inside the subway: - Duomo (MM1 and MM3) - Loreto (MM1 and MM2) - Cadorna (MM1 and MM2) - Centrale (MM2 and MM3) - Garibaldi (MM2). To get the monthly ticket you can go to any newspapers'stand inside the subway stations. Here you can get a form (there is usually a bounch just ouside them) or sometimes we have some of them at our ESN office. You have just to fill the form and give it to them with a picture and possibly a copy of a certificate saying you are studying at Politecnico (you can get it at your Studesk). You could be asked to show an ID.
For further information: ATM website