A spawner, also known as a monster spawner, is a cage-like block that can spawn mobs. When created, it holds a miniature, spinning version of the type of mob it spawns. Spawners are transparent, but they behave like leaves by diffusing the light coming from directly above. They are similar in size to a block but slightly smaller. If broken with a pickaxe, a spawner drops 15-43 experience. When mined with anything else, it drops nothing.
In Bedrock Edition, a spawner can be obtained in the creative mode by taking it from creative inventory, by using the /give command, or by using a pick block. It is initially empty, but it can be configured to spawn a desired mob by using a spawn egg on the placed block. You won't find spawners in survival mode, even with silk touch. You can find spawners in dungeons, mineshafts, woodland mansions, strongholds, nether fortresses and bastion remnants.
The spawner spawns mobs in a 9×3×9 volume (see § Mechanics) around it when the player is within 16 blocks spherically. The spawner attempts to spawn four mobs around it, then waits from 10 to 40 seconds before spawning more. As it waits, the mob inside the block begins to spin faster.
Just like configuring spawners, you can disable them if needed. It depends on which entity it spawned. For a spawner that generates mobs that spawn only in dark conditions, a torch placed on any side or top of the spawner is sufficient to disable it. For a blaze or silverfish spawner, a light level of 12 is required to prevent spawning. A spawner is also disabled by filling the spawning volume with solid blocks.
A. You can find spawners in all these locations: dungeons, mineshafts, woodland mansions, strongholds, nether fortresses and bastion remnants.
A. A player being in a 16 block radius of the spawner is enough to activate it.
A. Magma cube spawners are the rarest of all naturally generated spawners.