Details
The Wither skeleton skull is a rare drop of Wither skeletons. For spawning a Wither, you need 3 Wither skeleton skulls. Place 4 soul sand in a vertical T-shape, then place three wither skeleton skulls on top (see the picture above).
Heads are only available in Creative mode, except The Wither Skeleton variant which is a rare drop from the respective mob.
The main use of heads is for decoration.
The player can also wear heads as disguise, similarly to pumpkins.
Heads are used in the crafting of Firework Stars. Firework rockets crafted with said stars will have an explosion shaped like a Creeper face.