It's agreed before you sign to lease the car. You lease a car, price €70,000, lease company agree to take back the car for €35,000. Your monthly payment is around €1,200 per month. You may/ may not have to pay for service cost (might be included in monthly payment), you will have to pay for all non-service items.
They will usually agree a certain milage that the car has to be returned by. ie. 3 years and 100,000 kms, every km your over in the 3 years will cost you a €uro.