How do loans work?? HELP!!!?

ok i know that i need a co-signer because i am only 18 but i would like to get a car and i know that i will have to take out a loan but how does that work do they give me the loan in cash or how do i actually recieve the money. I would like to buy a car used from craigslist or a friend but if i need a loan how does this all work i am confused some one please help me