10k down payment how much a month

If you're trying to calculate a monthly payment, there are all sorts of free websites that will do this for you. But your down payment amount means nothing if you don't know how much you're borrowing, what the interest rate is, or how long you're borrowing the money for. Let me put it this way: if you're buying a $10,000 car and your down payment is $10,000, then your monthly payment is... zero.

If i put down 10,000 on a s550 how much is my payment

?

Again, it depends on: how much you're paying for the car, how long you're financing it and what interest rate you qualify for. Only the dealer or a bank can intelligently answer this question for you, as I don't have access to your credit history.