How long does it usually take to get a Green Card for living in USA?

i’m a 16 year old student, studying in America costs too much money, but i’m hoping to live over there once i’v finished college. i currently live in London

Thinking ahead a bit (5 years ahead lol) i have heard that getting a green card to live in USA is really difficult and takes both time and a bit of money.

how much time does it take to get one? from beginning the process to being accepted. much paperwork?

and how about Canada too?