How do you get to Williamsburg Brooklyn from Jamaica Station?

Again, there are a couple of stations in Jamaica, Queens, so I don't know which one you're talking about: there's the Jamaica-179th Street stop on the F line (of the B-D-F-V, the orange line), and there's also a Jamaica Center Parsons/Archer stop on the J-Z (of the J-M-Z, the brown line) and E (of the A-C-E, the blue line).

The J-Z (the brown line) goes from Jamaica Center Parsons/Archer through north Brooklyn, and you can transfer to the L at the Broadway-Eastern Parkway Station. Take the L to either Grand Street, Graham Avenue, Lorimer Street, or Bedford Avenue. All of these stops are in Williamsburg.

If you are talking about the Jamaica-179th Street stop, then: take the F from Jamaica-179th Street to the Briarwood Van Wyck Boulevard stop, and transfer to the E. Take the E to either Sutphin Boulevard Archer Avenue or Jamaica Center Parsons/Archer, and transfer to the J or Z. Take the J or Z to the Broadway-Eastern Parkway Station and transfer to the L.

See the Related Link below for a complete map of the NYC subways.