Please tell me the difference between zit and cyst?

Infection vs not: A "zit" or pimple is a tiny infection in a pore. The white stuff inside is pus. It's basically a very small abscess. There are many different kinds of cyst, but basically it's a walled off sac of fluid, but not an infection. Cysts can sometimes go away on their own, sometimes need surgery. Acne is generally treated topically (soaps and creams) and sometimes with oral antibiotics.