Dave,
The torque is the "turning force" the motor has. It is the force avilable at the motor shaft at the voltage specified - that's what you need to know as well as the torque - what voltage is it referenced to. A lot of motor manufacturers quote it at 14.8 V. It's usually pretty linear down to zero volts so if it's quoted at 14.8V you can get a pretty good Idea what it will be at 12V (about 12/14.8 of the torque).
For cars it's quoted in N-m, which is no good for slot cars because the scale is too high, so they use g.cm. Imagine putting a lever on the motor shaft 10cm long and putting 20g on the end that would be 200 g.cm torque (it's not grams per cm, this is wrong - it grams x cm's).
When you go through a gear reduction, you multiply the torque by the gearing ratio, if it's 1:3, the torgue on the wheel shaft is 3 times higher and the speed three times lower. The final driving "force" then depends on the tyre outer diameter...a smaller wheel gives higher driving force.