The Iron Golem is an friendly NPC that will spawn in villages or created by the player, hitting it will cause it to be aggressive.
We need to create one, this requires 4 blocks of Iron and a Pumpkin. The crafting table is not required to make the Iron Golem itself, but to make the iron Blocks.
An Iron Block as a block made of 9 Iron, so 9x4 is 36 Iron. Iron is found in caves, it's a common ore you can easily find. 36 shouldn't be a hassle
Pumpkins are usually found in Mountains or just grassy areas. Finding these Pumpkins is all chance.
Here is how you want to build the Iron Golem:
http://vignette1.wikia.nocookie.net/minecraft/images/d/d6/CI...Once done, it should suddenly pop out, and the achievement should unlock!