Minecraft wiki entry for How_to_play, associated text: The pickaxe is good at breaking hard blocks like cobblestone, iron ore, or furnaces.
The axe is good at breaking wooden blocks like logs, planks, or crafting tables.
The shovel is good at breaking loose blocks like dirt, sand, and gravel. A shovel can also create a path by using it on grass blocks.
The hoe is required for tilling dirt into farmland to plant crops.