Using the GAD FP, you go up to a FP attraction and enter your special card into the machines. Then the machines will spit out FPs that will be valid immediately. So you insert your GAD FP card at 9:30AM, the FP return window for that ride would be 9:30AM-10:30AM.
Using the GAD FP, you can choose any combination of rides within each "group", and you are able to get between 2 and 4 rides from each group.
So for example at Epcot, Soarin and Test Track are in the "Donald" group and Maelstrom, HISTA, Living with the Land and Mission Space are in the "Daisy" group. It wouldn't make sense if you get 3 FPs from each group and not be able to repeat a ride for the Donald group. You can get all 3 Soarin, all 3 TT, 2 Soarin 1 TT or 2 TT 1 Soarin, as well as 3 of any combo from the "daisy" group. Any mix and match within the groups is fine.