Janet,
You can read about Fantasmic at Disneyland here on the DIS:
Disneyland FANTASMIC!
Brief WDW Fantasmic Overview
Basically...
Fantasmic debuted at Disneyland back in '92 or '93, taking place on Tom Sawyer's Island, with scenes on the river also. The story is about Mickey's imagination, and takes us to some Disney classics, using water screens spread out like fans (there are 3 of them) that show popular characters. Live action takes place on the island & on the river. The story takes a dark turn when the Disney villains try to take over, with the climactic fight between Mickey & Malificent as a dragon. The show is full of music, choreography, and pyrotechnics. Guests sit on the ground or stand by the Rivers of America, from the Haunted Mansion to the Riverbelle Terrace.
At WDW MGM Studios, there has been an amphitheater built just for this show. People get to sit on benches and watch the show, which is very similar to the one at Disneyland. There are a couple of scenes that are different, and the boats/ships used at WDW are smaller, of course. Disneyland uses the Mark Twain and the Columbia ships, and the amphitheater river stage just doesn't have the room for such big ships.
Disneyland fans will go down saying that "their" (or is it "our") version is much better.
Both versions have their strong points. In my opinion it's the show at Disneyland, while at WDW it is the amphitheater seating.