General rule #1: Every job needs a job site located within the worker's territory blue circle*. Even training requires a punching bag and the repair job requires, well, broken structures to repair.
General rule #2: If the job produces a item, then it needs a place to store the items. For some jobs, the job site itself is enough to store the produced item (Log/Mine/Excavation sites). Otherwise, you need a separate Harvest Box.
Farming and livestock job sites can technically store the produced items but they don't go inside them automatically so you need a separate Harvest Box anyway.
General rule #3: Only a limited number of NPCs can work in a given job site at the same time. For most job sites this number is 3, though exceptions exist like only 1 worker for the Breeding Farm, and 1 worker for every 4 plots in planters (1 worker for small wood planter, 2 workers for big stone planter).
You might still want to assign additional workers to cover for down time. Workers will rest for a short while after each "job action" and they also take time to travel.
General rule #4: No tools are needed to work job sites. Your NPC can equip anything, or nothing at all. There's a reason why some of the job sites require tools as part of their crafting recipes. It's abstracted away as the NPC grabbing the tools from the site.
General rule #5: All NPCs can work any job. This includes animals. Yes, you can put rabbits and chickens to work farming and mining and logging, and pigs to raise pigs.
Some complications might arise from NPCs that can't move like the Mermaid on land or the Ent Queen. And of course Yona and Man can't work, but they're PCs.
The Food job just fills food boxes inside a worker's territory. Effectively, each time they perform a "job action", they make the food value number go up in a Food Box they choose. The number just goes up "magically", with no actual food item being produced or consumed.