Malpensa it's the main international airport (Milan Malpensa, IATA: MXP). The airport has two terminals, with Terminal 1 being the largest (international and intercontinental flights). Terminal 2 is used by a number of budget airlines. The two terminals are connected by a free shuttle bus service (running approximately every 20 minutes).
Malpensa Express Trains - malpensaexpress.it - is the only frequent railway link between Malpensa and central Milan. The Malpensa Express Trains between Malpensa and Milano Cadorna is recommended as the easiest and fastest connection if you travel from the terminal 1 of Malpensa airport to the city centre. Trains leave every 30 minutes from Terminal 1, arriving at Milan's Cadorna train station after 40 minutes (the Cadorna station is connected to Milan's subway network, at the intersection of the red M1 and green M2 lines).
Buses leave approximately every 20 minutes for Centrale Station. Travel can take from 40 minutes to 1 hour or more. Buses are the best bet if you arrive at Terminal 2. You can also check these websites: www.malpensashuttle.it, http://www.terravision.eu/ Using a taxi to get from Malpensa to the city centre is expensive.
Some European or national flights arrive at Linate Airport (IATA: LIN). This small but rather efficient one-runway airport is very close to the city centre (7 km). Buses 73 and X73 outside the terminal building goes to San Babila Square, in the city centre, which is served by metro line MM1.
The bus runs every ten minutes and costs €1.5. Check it here: www.atm-mi.it
Taxis from Linate to the city centre cost around €12-20 depending on traffic conditions.
Some budget airlines fly into Orio al Serio Airport (IATA: BGY). About 45km far from Milan, near the city of Bergamo. Ryanair refers to this as Milan Bergamo Airport.
Trains to Milan leave from Bergamo station, which you can get to by shuttle bus or taxi, but is quite far from the airport.
Trains from Bergamo to Milan run every 30-60 minutes and take around 1 hour. Adult one-way fare approx €5.
Bus Services leave for Milan from immediately outside the arrivals section of the airport.
Tickets are sold in Orio Al Serio Airport in Bergamo and at the Central Train Station in Milan.
Taxis will set you back maybe €100 from Orio to Milan.
The main railway station in Milan is the Stazione Centrale, Piazza Duca d'Aosta, is run by Trenitalia. Out of the station you can find the green and the yellow underground lines (M2,M3) and other transport means.
The Milan Porta Garibaldi Station is a major station in the city of Milan, located just to the north of the neighbourhood known as Porta Garibaldi (formerly Porta Comasina and a gate in a former wall of Milan), in the Piazza Sigmund Freud. The station is run by Ferrovie Nord di Milano.
The underground part of the station is located on the Passante railway. Lines S1, S2, S5, S6 and S10 of the railway stop there. You can also find the green underground line (M2).
Milano Cadorna is a commuter railway station located near the Castello Sforzesco in Milan. Run by Ferrovie Nord, it connects the city of Milan with the suburbs and with smaller cities like: Varese, Como, Novara, Brescia and some more.