This Altar is not made in a crafting table. You make it by placing blocks in the real world. Place two cobblestone and one wooden plank in a line. Then, get the Necronomicon and shift right click the wood. Now you have your altar.
The altar is used to summon minions. If you right click on the altar you can see some slots. Five slots in the middle and two slots on either side. Place a Jar of Blood in the left slot, and a Soul in a Jar in the right. Once you have placed all the parts, shift right click the Summoning Altar to spawn your minon.