Vehicle leasing is nothing other than a method of paying for the use of a car, truck, or van over a predetermined period of time. It sounds a little like renting, but don't confuse the two because they are actually quite dissimilar. You can rent a car for a time period as short as a day, or even just a few hours; leasing generally starts with a period of 24 months and doesn't allow for easy termination or the swapping of vehicles.
When you take on a lease you negotiate a purchase price with the dealer just as you would if you were buying a vehicle. This is not particularly well known and dealers are known to tell customers that, because it's a lease, the price is non-negotiable. This is just not true. In fact, the only time you would not be in a position to negotiate the price is when the dealer is offering a special deal in which the price and various other features of the lease are already geared towards attracting your business.
Once you and the dealer have agreed on a price, and the lease contract has been signed by you, the dealer then sells the car to the leasing company for that particular price. It is the lease company then leases the car to you based on that price. Because of this, price is the all-important factor in what you will end up paying in monthly payments.
Remember that the dealer is not the leasing company. The car dealer is merely acting as an agent for the leasing company. You won't actually deal directly with the leasing company until you begin to make the monthly leasing payments. The dealer just works out the terms and conditions of the leasing agreement with you and is, in effect, just acting on behalf of the leasing company. For providing this service the leasing company typically pays the dealer a commission, which is added to his profit on the whole deal. Once the lease contract is signed, your relationship is now with the leasing company and no longer the dealer. The only exception is if you have an issue with the car or vehicle itself.