Pins 2 & 7 require your 12V through the thermostat, Pins 1 & 8 get the 120V supply and Pins 3 & 6 go to the pump.
The Relay base you have will most likely be numbered to match your Relay pins, i.e Pin 1 on the base will go to Pin 1 on the Relay etc, but it could also be marked A1 & A2 for the coil pins depending on what manufacturers socket you have. All of the NTE sockets I have seen are marked Pin for Pin.
If in doubt, remember that the polarisation keyway in the middle of the socket points between Pins 1 & 8, if you hold the socket with the keyway pointing towards you, the pins are always numbered counter-clockwise.
The Thermostat is normally open, therefore the Relay is not normally energised, ergo neither is the Pump.
When the Thermostat closes, i.e the measured temperature drops below it's set point, the contacts on the Thermostat close, passing the 12V to the Relay coil, thereby energising it. When the relay contacts close the 120V supply is fed to the pump.
If the Pump has an Earthing (Grounding) point, make sure you carry an Earth (Ground) wire to it along with it's wires from the Relay. Put the Relay and associated socket in a plastic box, with a lid that can only be removed by undoing screws, and gland/strain relieve the cables going into and out of the box. Mount the box on the wall well out of the reach of water.
It will also be a good idea to put a fuse holder in the box with the correct rating of fuse for the pump, take your 120V supply to the fuse and from there to the relay and your 12V power supply, that way if something goes wrong, it's not going to cause a fire or anything.
Hope this helps you out