The hub of traveling in Boston is the "T". The "T" is made up of four train lines, Green, Blue, Red and Orange.
The lines run as shown below, and they come together at the Park Street (right next to the Park Street Church),
Downtown Crossing and Government Center stations. At these stations you can change lines.
Fees for the T are cheapest if you get a monthly pass.
If you are located outside of the Boston area, you can use the Commuter Rail to get in, and then connect to the "T".
The Commuter Rail has two hubs, North Station and South Station. Generally, communities north and northwest of Boston,
e.g., Rockport, Newburyport, Haverhill, Lowell, Fitchburg, etc. are served by North Station, and communities south
and west of Boston, e.g., Worcester, Frankin/Dean College, Providence, Middleborough, Kingston, etc., are served by
South Station. Fees for Commuter Rail are definitely cheaper if you buy your tickets at the stations (or
online) rather than buying them on the train.
For more information, visit the MBTA website.