Minecraft (Pocket Edition)
Usage / Purpose
In Creative Mode you can place a Monster Spawner on the ground and then place any Spawner Egg type into the Spawner by tapping on it. This will then place a small spinning image of the Egg type in the Spawner and the Spawner will continue to generate/hatch unlimited copies of that Egg type until it is deactivated by breaking or by placing a Torch on top of it.
In Survival Mode, Monster Spawners are found in Dungeons, Strongholds and Abandoned Mineshafts. Dungeons usually contain Skeleton, Creeper or Spider Spawners. Strongholds contain Silverfish spawners. Abandoned Mineshafts typically contain Spider spawners.
Drops / Yields
Although Monster Spawners can be broken in both Survival and Creative Mode, they do not drop anything. Additionally, they cannot be crafted.
Monster Spawners will continue to generate Mobs of their chosen type (indicated by spinning creature inside the Spawner cage) until the Spawner is deactivated. Spawners are deactivated by placing a Torch on top of the Spawner to increase the light level, or by breaking the Spawner (any tool can be used).
A broken Spawner simply disintegrates and does not drop anything.