I'm a young man and have never even dabbled in car purchasing... how do you buy a car?

Like I get new cars. You just walk in with a down payment and sign a contract and pay every month. And isn't leasing the worst thing you could possibly do financially because it ends up costing you so much more in the long run? And how do you buy a used car? Do you really have to have the ENTIRE payment of the car because you can't finance a used car? It's all very confusing via /r/cars http://ift.tt/2tsYi11