Up at the top of the page (of the index to various posts), you'll find a lik to Frequently Asked Questions which will give you a good overview of
DVC.
Basically you purchase a real estate interest that is expressed in terms of points. Current purchase prince from Disney is $75/point and a minimum new contract is 150 points.
While points can be used for things like
DCL, generally your best value is for using points to stay at a DVC resort. If you are only looking at purchasing DVC for using on DCL, I'd be very careful to run some numbers to see if it makes sense financially - my gut reaction would be that it probably doesn't.