A GPS antenna is useless.
If you mean that you have a "hockey puck" type GPS, not just an antenna, that's something else again.
In that case, if it puts out NMEA
18x or RS-232, with a standard DB9 serial
connection, you connect the RX line form the GPS to the TX line on the PC's com port. And the TX line from the GPS to the RX line on the PC's com port.
You'll need to document what wires come out of the GPS. On the DB-9 side, that's usually pins 2 and 3, and if you get them backwards, no harm, just reverse them again.
Both the GPS and the com port will need to be set to the same protocol (usually N-8-1) and speed (usually 4800bps?) as well.
If all that sounds like greek to you...Well yeah, it's like poker, a very simple game
with simple rules.<G>