Justin Herman Plaza is easy to find. Just look for all the people.
If you can't find the corner of Market and Embarcadero in San Francisco, please make sure you are signed up for the Beginner division...
If you need driving directions, try Google maps and search for 1 Market in San Francisco, CA.
Alternatively, take BART or Muni to the Embarcadero station, or AC Transit across the Bay to the terminal and walk North to Market, then East towards the Bay.