Please explain what a down payment is!?

You can consider a down payment as "trust me" money. You put your own money into the purchase up front, showing intent to fulfill the purchase contract. If you don't keep up the payments and the car gets repossessed, the lender can re-sell the car with less chance of taking a loss because he has the money you already put into the car as a cushion. A down payment also reduces the amount you need to finance, which may qualify you for financing you otherwise couldn't get, or a shorter payoff period, or possibly a lower interest rate.