The air cell is in the fat end of the egg. The idea of putting the pointy side down is to keep the air cell up so the air does not try to migrate to the other end of the egg if you accidently put it pointy side up. It is true that hens do not stand the eggs on end so the pointy side is never up. There may be other advantages (I don't pretend to know everything that goes on inside an egg during incubation) but if you put the pointy side down every time, you will not mess up. The people that hatch eggs for a living, the hatcheries, do it this way. If another way was better, they would do it another way. That said, I think there are some small incubators with turners that you just lay the egg down, not put it pointy side down. I don't know this for sure since I don't have one of them.
The egg needs to be turned regularly during incubation to keep the yolk or developing chick from settling in next to the egg shell. The egg shell is porous so if the yolk or developing chick touches the side and loses the insulation provided by the egg white, the yolk or chick can dry out through the porous shell and stick to the inside of the egg shell. That is a fatal problem. By the time you get to lockdown, the chick is so large inside the shell that it is going to touch anyway. You can quit turning and just raise the humidity to take care of this.
Depending on how you are doing it and the incubator you have, there are different possible ways to rotate the egg. You are trying to turn it a full 90 degrees. If you have an automatic turner, they'll take care of this for you. If you have to do it by hand, you can put and x on one side of the egg and an o on the other so you know which side is which. Then you can tilt the egg in the carton 45 degrees one way to the other to get the full 90 degrees. If they are in cartons and your incubator allows it, you can set a block of wood under one end of the carton to get the 45 degrees, then switch ends of the carton with the block of wood whenever you turn them. I've heard of people using the block of wood method on their entire incubator, but I'm not sure how they handle the water reservoirs for humidity when they do that.
