Assuming you mean jump-starting a car with a drained battery:

The short answer is that you attach the red clamps to the positive terminals and the black clamps to the negative terminals, and then you should be able to start the car normally. Intuitively, you're just hooking up the good battery to the car with the bad battery, via cables. This would also work with just a new battery.

Jumper cable boxes tend to have instructions, which may tell you to do something slightly different.

And exercise general safety - don't stand in front of the engine while someone is starting the car.