DVC is a vacation ownership plan - like a timeshare, but not tied to a specific resort or week of the year.
You get an allotment of points every year that you can use at Disney DVC properties (at WDW, DLR, Vero Beach, Hilton Head and Oahu). If you buy from Disney, you can also use those at non-DVC Disney properties (including non-US disney parks as well as non-DVC at WDW and DLR and DCL) as well as other timeshares through an exchange.
What you should do is guesstimate how much you would spend on lodging over the next 10 years or so and compare that to what you would pay to 1) buy the points needed for the kind of roo you like 2) pay the dues each year on those. There are a bunch of threads about such a cost benefit analysis.
If you go annually to DLR or WDW resorts and stay at moderate or above, you'll usually find a DVC membership breaks even somewhere in those first 10 years. After that, you should expect to spend less than you otherwise would have.
DVC is a wonderful thing if you 1) go to WDW at least every other year (or Hawaii, Vero Beach, HHI or DLR) 2) you can afford the costs up front or don't have to take a second mortage to finance your "Disney" habit and when you do travel, you stay in at least a moderate or, if your family has more than 4 members, you require a suite or larger accomodation. If you really want the down and dirty, sign up to receive the free DVD to learn more about.
Exactly! Perhaps you are planning your first trip, and think that "joining" DVC will give you some discounts or save you money in some other way?
It won't.
As stated above, it's basically a timeshare. Once you go, and IF you decide you'd like to go on a regular basis for the rest of your life, and IF you want to stay on-site each time at a Disney resort, THEN and ONLY then is it something you should consider.