A train on the green (M2) line
Milan's underground, la metropolitana, is commonly referred to as la metro for short. It only consists of three lines, the passante (Urban trains, which also connect towns outside Milan to various stations within the city) and two more lines which are in the works. Once you get used to it it's a very quick and cheap way of getting around the city.
The three underground lines are imaginatively called M1, M2 and M3, but people refer to them more by the colour of the line. M1 is red (rossa - as the world for line, linea, is feminine, the colour takes on the feminine form), M2 green (verde), and M3 yellow (gialla). The various 'S' lines of the passante connect the many train stations in Milan, and commuter towns outside it, the trains pass less frequently than the metro. The M4 (which will be blu, dark blue) and M5 line (lilla or lilac) are being constructed at the moment. The blue line will connect the city of Milan to Linate airport in the east of the city, and is due to open in 2015; and the first section of the M5 line is expected to open in a few months.
A single ticket for use within the city limits
The underground in Milan is very cheap, and it costs the same as the other forms of public transport in the city. A single ticket will now cost you one Euro 50 cents, which is valid for one journey on the underground or passante, within the city limits, and of a duration of up to 90 minutes (it used to be 1 Euro for 75 minutes). There isn't a maximum number of stops the ticket is valid for, and within the city limits there are no fare zones; but outside the city limits (which are clearly marked on the maps you see on the underground) you will be paying more to travel. If you are making 3 or more journeys during a 24 hour period it's worth buying a daily ticket (biglietto giornaliero) which costs 4.50 Euro. What I usually buy is called a carnet, it's 10 journey ticket that costs 13.80 Euro. That way I save a little bit of money, and I don't have to buy a new ticket every time I go on the underground. Tickets can be bought at edicole (newspaper stands) and tabbacherie, and at the big red multi-lingual machines at each stop. The tickets for all forms of public transport in Milan are exactly the same, there are still some older tickets in circulation, but there's no difference between a ticket that you bought for a tram journey to one that you bought for a metro journey. Urbano tickets (those valid for journeys within the city limits) are also all the same, so you could use a ticket that you bought, say when you arrived in Milan at Stazione Centrale, for a journey starting from the Duomo stop. Tickets must be convalidated by going through the barriers on the way down to the platforms.
Esthetically speaking, the metro trains in Milan aren't the nicest ones in the world, especially the green line trains which finish outside the city limits. There are a few fancy new ones though, with bilingual announcements and little screens which show what the current or next stop is, and the other transport links available from that particular stop.
A sign at Cadorna for trains going to Cologno Nord/Cascina Gobba/Gessate
Most of Milan's train stations (including Centrale) are on the green line, you can get into the centre of Milan on the red line by stopping at Duomo or San Babila. Yellow will get you to the Montenapoleone area of town, and it also goes through Centrale and Duomo.
If you're planning on coming to Milan soon I hope my little guide to the Milan metro has helped!
Some useful words:
La metro (shortened from metropolitana) - underground/tube
Il treno - train
La fermata - stop
La stazione - station
Il biglietto - ticket
L'abbonamento - season ticket (weekly, monthly and annual abbonamenti are available)
La linea - line
La direzione - direction
Il binario - platform
Il/la prossimo/a - the next
- La prossima fermata - next stop
- Il prossimo treno - next train
Il collegamento - connection
Convalidare - to convalidate