From Fiumicino airport, take the train to Termini and then the Metro, Linea B, to Basilica di San Paolo.
From Ciampino airport, either take the airport coach to Termini, or take the local bus 720 to Laurentina which is at the end of the Linea B Metro, just 5 stops from Basilica di San Paolo.
From the Metro: Turn left once you are through the turnstyle at the Basilica San Paolo station, walk past a line of market stalls (open during the day), cross Via Ostiense at the traffic lights and continue in the same direction, crossing a smaller road and then passing (on your left) the big Poste Italiane building and the administrative centre of the Bambino Gesu hospital. After a walk of about five minutes from the Metro Station you reach a crossroads; the Beda is the large, white-ish building on the diagonally opposite corner. .
From central Rome, either take the Metro to Basilica di San Paolo, or the No. 23 bus which stops outside the college.