Villager job blocks in Minecraft are blocks that determine a villager's profession. These blocks can be interacted with by villagers to take on or change their profession, and each block corresponds to a specific type of villager. Here's a list of some of the key villager job blocks and what they do:

1. Composter (Farmer) Villager Profession: Farmer Purpose: Farmers harvest crops and breed animals. They can be traded for food, enchanted books, and other useful items. The composter is used by villagers to become farmers and is often placed near crop fields.
2. Blast Furnace (Armorer) Villager Profession: Armorer Purpose: Armorers craft armor for players. They can offer armor sets and upgrades, like enchanted armor. The blast furnace is used by the armorer to craft and repair armor.
3. Fletching Table (Fletcher) Villager Profession: Fletcher Purpose: Fletchers craft bows, arrows, and crossbows. They can trade various types of arrows and bows. The fletching table is used by the fletcher to create and upgrade archery-related items.