This achievement can be earned easily in the tutorial area.

After completing/skipping the tutorial, proceed up the cobblestone steps and walk straight ahead towards the large building at the end. On the right are some pumpkins, and four blocks of iron stacked perfectly to make an iron golem. The game gives you a tutorial on how to make them.

Simply place the pumpkin on the already setup iron blocks and enjoy your achievement.

If you need any help PM me.