The wither is spawned by placing 4 blocks of soul sand and/or soul soil in a T shape (see image on the right in the "Behavior" section), and putting 3 wither skeleton skulls on top of the three upper blocks. The last block placed must be one of the three skulls and can be placed by the player or a dispenser.

Why can't I spawn the wither?

You need to set up the 4 soul sand in a T-pose and place the three skulls on top of it with some space separating each of them. ... These blocks must specifically have to be blocks of air, meaning that putting something like sand, grass or anything else will ruin the structure and will prevent the wither from spawning.

Can you spawn the wither in creative?

Yes, you can spawn withers in creative mode. How do I get wither skulls? you get them by killing some wither skeletons, but make sure that your sword has Looting III. ... You'll need to gather three wither skeleton skulls by killing skeletons in the nether.