Since there is no train station in Portofino, take the train to the nearby Santa Margherita Ligure. There run 1-2 trains per hour. The journey takes between 40 minutes and 1 hour. For a ticket you pay € 3.30 to € 6.50 per person (one way, 2nd class). Better check the train timetable between Genoa and San Margherita Ligure, Portofino in advance.
From the station in Santa Margherita Ligure is a good bus service to the center of Portofino. Bus N° 82 runs every 15 minutes between S. Margherita Ligure station and Piazza della Liberta in Portofino. The journey takes about 20 minutes and costs € 1.50 per person. The bus ticket is valid until 100 minutes after validation.
TIP: Buy your bus ticket in advance at one of the outlets or at the ticket machine. On the bus, you pay double.
How do I get to the train station from the cruise port of Genoa?
If you are docked at the cruise port of Genoa and you want to make an excursion by train, then you best depart from the main railway station Stazione Principe. This is within walking distance of the cruise port. From Principe metro station, walk right. Follow the street and turn left. Soon you arrive at Piazza Acquaverde, where you can see the entrance of the station on your left.