If you cannot afford to pay for the car outright in cash, you will need to finance at least part of the vehicle cost.
Basically, that means that you're getting a loan through a bank, credit union or car dealership. The lender determines what interest rate you will pay based, in large part, on your credit score (the higher your credit score, the lower interest rate you can get). The length of the loan (e.g. 48 months, 72 months, etc.) largely depends upon the monthly payment you can afford. The lender holds the car title until you pay off the loan.
Financing is available through banks, credit unions and online lenders. If you are purchasing your vehicle from a car dealership, you can also take advantage of arranging financing through them. But be aware that sometimes the price for this convenience is a higher interest rate. To get the most favorable loan terms, shop around.
If purchasing your car from a dealer, he may offer you "spot delivery", which is the option to take possession of the vehicle as soon as you've committed to buying or leasing it, before the financing has been finalized. This can end up costing you in the event that your financing is denied. Therefore, it is recommended that you wait to take possession of the car until your financing has been approved. Read more about the potential pitfalls of spot delivery.
Next Step: Buying from Individual vs. Dealer