Just connect the +12 and gnd wires to a power source, and connect the TX on your card reader to RX on the PC serial port (pin 2 on the 9 pin 'D')
Fire up a terminal emulator (like Hyperterm), and you're all set. These readers usually are configured for 9600 baud, so make sure your Hyperterm is set likewise.
Now when you bring the tag close to your reader, the ID string would be displayed on Hyperterm. This ID is usually also printed on the tag.
Also, when a valid read happens, you'll get a momentary signal on the beep pin.
Regards,
Anand Dhuru