A ground point is like the earth line in a power plug. The ground on a guitar will just get rid of any unwanted signals = leading to a guitar with less hum. THe more you ground, the less the fuzz basically.
It doesn't matter what guitar you have, there is still a basic circuit at least involved and ground can be anthing metalic that is not a part of the circuit. So in this case, the stoptail and TOm bridge of the SG can ground to the back of pots, shielding, pickups, and the pots themselves should be wired to ground.
P.S I learnt by opening up my guitars and staring at the wiring seeing which went where. And from there I think you'll find the ground spots.