Having flown in & out of Malpensa since 1993, certainly there have been many changes with the new terminal.
From the USA on American Carriers, you should be arriving at Terminal 1.
If you are flying into the airport you can basically get to the city center by 4 main means of transportation.
Of course check the schedules as certain times of day the schedules change.
Taxi– cost is about 70-80 euro. Travel time is anywhere from 45 minutes+
Metro– You can take this to various stops, but one is the Central Railway Station (Stazione Centrale) for 10 euros per adult. Children 4-12 travel for 5 euro and children under 4 go for free. Trains take anywhere from 43 to 52 minutes. Trains leave every 30 minutes.
Bus– The Malpensa Express costs about 10 euro one way and takes you to the Central Rail Station (Stazione Centrale). The bus leaves normally every 20 minutes and takes about 50 minutes.
Rental Car– All major rental cars are located on level 0. The arrivals are on the same level. I would strongly recommend joining a rental car program that allows for “express pick-up” as the lines can tend to get long, especially in the morning.
Flying out of Malpensa:
Most flights back to the USA will leave in the morning. There is a Sheraton Hotel directly at Terminal 1. Having stayed there numerous times I can highly recommend staying there.
If you have a rental car, you can park the rental in front of the hotel and drop the bags off as they have “bell boys”.
Also nearby with free shuttle service is a Novotel and also a Hilton Garden Inn.
The departures are on level 2.