Taking the train from San Francisco Airport to San Francisco is a good way to get into the city center.
Bay Area Rapid Transit, or BART trains, run regularly from San Francisco airport to San Francisco. Follow signs in the arrivals halls to get to the airport BART station to get to the trains.
Tickets for BART trains can be purchased in the airport BART station at ticket machines. Fares vary depending on your final destination. The average price for a fare from the airport to the city center is $8.10.
The BART journey time from San Francisco airport to the downtown area is around 30 minutes.
Note that BART is not meant to serve the entire city of San Francisco, and only runs through the Mission, Civic Center, Union Square, and Financial District/SOMA areas.
If your hotel or final destination is outside of those areas, you will need to take a bus, street car, taxi, or walk after getting off of the BART train downtown or in the Mission district.