http://disneydebit.com/perks.html
I don't necessarily feel that it's vague. But I will tell you that you HAVE TO mention the discount BEFORE they finish ringing you up. We had a CM get all weird about it when I had her re-ring everything because I didn't know I had to mention it. I figured the blue, with castle and sparkles on it debit card I handed her would sort of clue her in. But no, you need to mention the discount so they can ring it in right.
Merchandise:
Your discount is available at select Walt Disney World® Resort owned locations and pin cart locations throughout the Resort.
Dining:
Receive 10% off at select dining locations below (restrictions may apply):
Disney's Animal Kingdom Lodge
Jiko (see restrictions)
Sanaa
Disney's BoardWalk Inn Resort
ESPN Sports Club
Flying Fish Cafe (see restrictions)
Kouzzina by Cat Cora
Disney's Caribbean Resort
Shutters at Old Port Royale
Disney's Contemporary Resort
The Wave
Disney's Fort Wilderness Resort & Campground
Trail's End Restaurant
Disney's Grand Floridian Resort
Citricos (see restrictions)
Grand Floridian Cafe
Disney's Old Key West Resort
Olivia's Cafe
Disney's Port Orleans Resort
Boatwright's Dining Hall
Disney's Saratoga Springs Resort & Spa
Turf Club
Disney's Wilderness Lodge
Artist Point (see restrictions)
Whispering Canyon Cafe
Disney's Yacht Club Resort
Captain's Grill
Disney's Hollywood Studios®
The Hollywood Brown Derby (see restrictions)
Hollywood & Vine (see restrictions)
Epcot®
Biergarten Restaurant (see restrictions)
Subject to restaurant operating hours and closures.
What to do: Use your valid Disney Visa® Debit Card and mention this offer to receive the discount.
Why: Save during your vacation while giving your family a delicious treat.
And etc all on that link above.
If you're used to putting things on a CC for rewards, remember that this means you're paying with your debit card. We finally used the debit for our big merchandise purchase because it finally hit me that 10% off was better than 1% back, LOL.