You want to connect the NMEA+ wire from the GPS to Pin 2 of the RS232/USB adaptor, and the 12V ground wire to Pin 5 of the RS232/USB adaptor.
Here is a link to some good information about the
RS232 connector:
DB9 Pinout
You will want to buy a female DB9 connector and solder the GPS wires to that, then plug the female connector into the male connector on the RS232/USB adaptor. Don't try to solder directly to the pins on the RS232/USB adaptor.