Same as any other gun except with an electrical charge igniting the powder rather than a firing pin hitting into rimfire/centerfire cartridge. The trigger completes a circuit with the battery, which ignites the powder and sends the pellets shooting down the barrels. From diagrams it looks like the doohickey wasn't designed to be reloaded.
Guns with electrical firing aren't unheard of though, they're just more common in things like very large guns like artillery or guns on a fighter jet. The famous M61 vulcan cannon for instance often has electrically ignited primers.