There are essentially two types of loans, loans based around a predefined number of monthly payments and those in which repayment is scheduled around some other factor (such as revenue, profits, payment in full, etc). An auto-loan is typically a loan that is based around a predetermined number of payments. These loans are referred to as installment loans.
So, what makes one auto-loan different from the next? How do you decide what kind you want? You may have noticed that often a loan with fewer payments also has a lower interest rate. So perhaps a 36 month loan will cost 5.5% interest per year, whereas a 60 month loan may cost 6%. Why the difference in interest rate and how does it effect you? The reason shorter loans have lower interest is because you are paying them back faster. The quicker the bank is repaid the less likely you are to default on the loan, and if you do default the higher the percentage of payments you've already made.
They try to encourage you to pay back the amount owed faster by offering a slightly lower interest rate. But that is not the only thing that saves you money. If the total amount owed is paid back more quickly, there is less interest applied to each payment. The less interest you pay the less you pay in total for the loan. This can save you thousands of dollars over borrowing for say 60 months instead of 36. Definitely something you should consider next time you consider buying a vehicle.