Snow Golems are created by stacking two blocks of snow atop each other, then adding either a pumpkin or Jack o'lantern on top. They resemble a snowman with a carved pumpkin for a head, although by using shears a player may remove the pumpkin head to make them appear as regular snowmen.
When in the warmer biomes of a Minecraft world, the temperature will cause Snow Golems to melt, as will contact with either rain, water, fire or lava, although certain magical potions will help them to survive in these situations.
These Golems will also move towards, and throw snowballs at, any nearby hostile mobs, and while their snowball attacks do no damage to any type of mob except Blazes (a mob indigent to the Nether, where the fiery environment is extremely detrimental to Snow Golems), this behaviour does have its advantages; first, mobs attacked by a snow golem will be knocked back a certain distance, and second, any mob attacked by a Snow Golem will be 'provoked' by it, turning its attention away from the player and on to the Golem. This makes them useful for distracting an enemy while the player either escapes, or attacks the otherwise-occupied mob. In addition, 'corralling' large numbers of Snow Golems is a handy way of making sure that nothing dangerous ever gets close enough to something important to do any damage.Another point of note with Snow Golems is that as they move, they leave a trail of snow in their wake. A player may break this snow using a shovel to collect the snowballs, which could be useful when in a biome with a lack of snow or ice.
It is technically possible for an Enderman's activity to create a Snow Golem, although the chances of this happening are astronomically rare; Enderman remove and replace blocks at random, so the odds on this occurrance are virtually nil.