Before you lease a vehicle, you're asked to decide on an initial rental. This is the amount you will pay upfront on the first month of your leasing contract, and it is typically 1, 3, 6 or 9 times the monthly rental. The higher the initial rental, the lower the monthly rentals.
6+35 is a 3-year contract, with 6 months initial rental. This means that you will pay 6 times the monthly rental in the first month, and then 35 monthly payments thereafter.
The initial rental is not a deposit and is not returned at the end of your lease.