DVC maintains
Points Charts (there's a link at the top of this page) that represents how many points are required for each DVC resort for any given time period of the year. There are "seasons" within the DVC charts that get progressively "more expensive" points-wise based on the peak periods at the different resorts (primarily WDW, but also DL now with the Villas the Grand Californian, and the 2 off-site resorts at Vero Beach & Hilton Head).
When you buy in with your membership, you purchase a set number of points that will refresh each year on the anniversary of your USE YEAR (for example, my UY is Dec 1-Nov 30th, and we have 350 points. Each Dec 1st I get a new set of 350 points to use). Within the DVC system you can bank and borrow points as well. If you know you won't be traveling in any given year, you can then bank those points into the next Use Year. Or if you know you will be traveling that year but need extra points because you've decided to bring friends along and need a larger villa, or you want to go at a "more expensive" time of year, then you can borrow points from the next UY.
The initial cost of DVC really gets spread out over the term of the contract vs a single trip like a standard cash reserved hotel room. There are also annual member dues to factor in to the equation, but once the purchase contract is paid for, that's all you'll be paying for the duration of your contract.
In the long run DVC can save money on accomodations when you factor the rising cost of hotel rooms and tax rates over time. Initially it is a large amount of money to pay out, but you'll probably really like it in years to come when you make a reservation and then don't have to pay anything for that reservation.
DVC maintains Member Services, which serves as our "reservation central". Simply call MS, tell them what you want and if there's availability, it's yours. They'll deduct the points from your account, and issue a confirmation letter. There are lots of ways then that you can track your points usage, from a basic excel spreadsheet to some fancy software programs that you can download.
Hopefully that helps a bit.