I wanna finance a car and I'm 18 with no credit what would I have too do?
Do you have a steady job or other means of repaying the loan if you are given one? Will another adult with good credit co-sign the loan for you? Are you buying a modest car at an average price? Otherwise, I would start by establishing a good record by having any bills like phones, power/water, cable, rent, and the like in your name and then, after about 6 months to a year, apply for a car loan (assuming you have paid your other bills on time).
You would probably need to get a co-signer on the loan. I usually don't advise anyone to do so. Check with your local bank for details. But your best bet is save up some cash and buy a cheap car for your first vehicle. Around $3-5K. Put some money aside for repairs too.
Get a good paying full time job and keep it for a year or more. Bum rides or ride the bus in the meantime.