The most important part is orientation. The campus is rather small, so it's actually very easy. If you arrive with the shuttle bus from JFK/UMass T station (red line), you'll walk straight into the CampusCenter. As the name suggests, this is the building that holds all kinds of important offices, like the Office for International and Transnational Affairs (OITA) for example. This is where you'll find Lurlene. The Student Service Center is here, too. You should go there on the day of the International Students Welcome Event and get a Student ID card - you'll need it for the gym and the library. Also, they offer special deals on sports and theater tickets for students here, so you might want to swing by every now and then. The university bookshop where you can get all your necessary books for class and stock up on notebooks, pens and UMass clothing, is right at the entrance to your right! The main cafeteria is also in the CampusCenter. Breakfast is pretty good, but they only serve it till about 10:00 so be aware :) The bagels are available for a little longer, but if you want to enjoy bacon&eggs, you gotta hurry :) The CampusCenter is also the only building with a full ocean view - I spent a lot of time here :)
Pretty much directly across from McCormack is the Science Center where they hold all the science classes (surprise!) and the next building on the left (so right next to McCormack) is Healey library. If you want to check out books, simply stop at the info on the second floor and get a barcode sticker! In the back of campus is the Administration building, which also includes the walk-in clinic (Health services). You might want to stop by there and show them your immunzation pass, otherwise the office will send you an email later and ask you to come in or else they'll hold your accound and you can't get any credits.... They are pretty nice over there, though.
Every building has some kind of café and rows of food and drink automats as well as ATMs. The café on the ground floor of McCormack serves Starbucks coffee, the bakery in the Healey library is pretty good and the main cafeteria includes a Burger King and a Panera (best sandwiches ever!)
The wi-fi on campus kind of sucks - it keeps disappearing. And the whole structure is a little odd. There's a nice background story which I won't give away just yet :) Let's just say the campus is funny :)
There's always something going on, so make sure you check the bulletin boards every now and then! And get a "welcome week" booklet to see what kind of activities are offered in the first two weeks! (they usually have movie screenings, barbecues and stuff...)