How does atmospheric pressure change with height in the atmosphere?why does it change?

Let's start with the basics. The atmosphere is composed of a mixture of gases of varying weights. These gases, while you may not notice it in everyday activity, do have m. The atmospheric pressure is, basically, the weight of all the gases above a certain point on the earth. So at sea level, you would have an atmosphere's height of air pushing down on you in a column. Now as you progress higher into the atmosphere, you have less of the gases of the atmosphere above you, and therefore less weight pushes down on you. This is why atmospheric pressure decreases with height. It's a very rough explanation I know, but I hope it helps.