Get off at Powell Street Station to exit to 4th and Market Streets. For 4th, turn right. Then walk 2 blocks south until Howard and turn left. You’ll find Moscone Center on the 700 block of Howard Street.
By Caltrain
If you’ll prefer Caltrain Station, get on the 15th, 30th or 45th lines and disembark at Third and Folsom. Walk one block north until Howard Street and you will find Moscone South on your left.
By Car
If you are directly travelling to Moscone Center from San Francisco International Airport, you can exit the airport from North on Interstate 101 and then you can follow the directions that can be found on the official website of Moscone Center.