The first referral is $200, after that it increases. You will get the offer online in your account once the person buys. You can then choose how you want it and yes it can be applied to your dues. I took mine in a Disney gift card and applied it to my then upcoming cruise.
It depends which state you live in, too. Some states don't allow members to get financially rewarded, for some reason. It is not Disney's fault. Unfortunately, Oregon is one of the states like this. Oh well. At least I got a nice card from DVC thanking me!