How do pimples and other forms of acne form?

I%26#039;m 13 years old amd i%26#039;ve been getting pimples around my nose and chin. I want to know how they form and how to get rid of them please. If this helps i get really sweaty from skateboarding all day.|||sweat mostly, since the sweat clogs your pores. other times its just puberty :P