Name Tag is used to name Mob, you can use the Anvil to write a name on the tag and then right click any Mob. Doing this will have their name displayed over their head. One of the ways of obtaining a name tag is in Chests located in Dungeons. They are also able to be picked up during Fishing. The third way of obtaining a name tag is through trading with villagers. When a mob has a name tag attached, they will also not be removed in the world. The only monster you are unable to use the item on is the Ender Dragon.