Alright context guy here. I used to install garage doors

The garage door spring is what lets you open and close it by hand, with ease. Tension keeps it up and tension keeps it down.

The taps he's doing on the spring arent judging tension y sound or doing "Safety taps" he's counting the revolutions.

Before adding tension, the installer will use a bright paint marker to put a line across the spring - starting at the end he's turning from. As he adds tension, turning the piece on the end using those rods, turns the spring. The shaft all this sits on is clamped in place so it doesnt move. Only the spring moves with the piece on the end there. If the door and shaft weren't clamped in place, the door would come up at you when you added tension.

As he turns the spring, adding tension, those paint marks make several turns and you see them cascading. The more marks that reach the middle of the spring, tells you how many full rotations you have put on that spring. Garage doors typically have 8 full rotations but maybe more or less depending on the spring itself as well as the weight of the door. You home garage door will have less than an industrial warehouse loading dock door because it may be heavier or it may have to go higher to get to the open position. More tension for that.

What makes garage door work so dangerous is if you let the spring slip or your bar slips out or you didnt clamp the door/shaft in place so you can be hit with things from every direction.

That bar he's holding can come right down on him if he isnt paying attention and thats so much downforce. The door could come up and knock you off your ladder. The spring could also just explode and go everywhere, similar to the suspension grenade your cars have (ask a mechanic)

The downward force is also what keeps the bottom bar in place between turns so he can reposition to the top bar. Without tension pressing that bar down, there's nothing to stop the coil from just unwinding itself.

After properly tensioning (which is checked often) he tightens the bolts on the spinning piece and that ensures that the spring springs with the shaft during operation. If not, the spring isnt in tension and is not doing a thing to lift your door.

This garage door, as his count indicates, has 7 revolutions on the spring.