16th Street is a minor arterial that runs East-West. It starts at the Bay near Mission Bay/UCSF's Mission Bay campus, and runs all the way up to Market Street in The Castro. The most notable thing that happens to 16th on its journey from the Bay to the Castro is that it crosses Mission Street right next to 16th and Mission BART. Also worth noting is a shopping center at 16th and Potrero (the Potrero Center).
Because of historical street grids, San Francisco's First Street through 11th Street actually run northwest-southeast. 16th Street is among the first few east-west streets. As a result, 16th Street intersects 7th Street just west of the freeway, and then goes on to cross Third Street. (14th Street is actually the first east-west street, but it's a lot shorter and is interrupted by obstacles such as the freeway, so there are fewer amusing intersections.)
16th Street is served by the 22 Fillmore bus line along most of its length.