The interest rate is usually determined by your credit history and the current market.
As for the loan, some require down payments, some don't.
Your monthly payment will be determined by the interest rate, the total amount of the loan, the down payment (if applicable) and the length of the loan.
If the loan is for 45,000 and you have 8% interest rate, the interest on the loan would be $3,600. This makes the total loan 48,600.
If you divide it over 60 months, your monthly payment would be approximately $810.00 a month.
But I can only guess because I don't know what you are trying to purchase or in what time period.
A house payment will also have PMI and house insurance included.
A car loan is a little more straight forward.