Just place it where you want the mob to appear. Animals will spawn tamed, unless you hold down the sneak key while placing. If you place this on a mob spawner, you change the mob it spawns.=
You need the “maphack” privilege to change the mob spawner.=
Removes specified mobs except nametagged and tamed ones. For the second parameter, use nametagged/tamed to include tamed or nametagged mobs, or a range to specify a maximum distance from the player.=
Default usage. Clearing hostile mobs. For more options please type: /help clearmobs=