They're talking about taking off when stopped on a hill. Pressing the clutch and releasing the brake will result in the car rolling backward down the hill until you get enough forward momentum going to take off. Newer drivers freak-out on the rolling backward bit.

I remember an earlier discussion on HN where different people around the world learned different techniques for preventing the rollback. I remember lots of Europeans saying that's what the parking brake is for. Here in the States we're taught to let out the clutch until it starts to bite and then release the brake. You may still roll backward a few inches but that's no big deal.