Jobs are high profile things, such as building a structure, or working a profession. Chores are the little things, like making a stew from vegetables (1 unit vegetable makes 4 units of stew) or tending a garden, field, or pasture. If it takes more then a season to accomplish, or uses a workshop it's probably a job. If it's something that needs to be done, or a minor action, it's a chore. Think as chores as maintenance, someone has to tend the fields and the animals, cook the food the make what little you may have last, or take care of children. Chores also do not have levels like professions do, you simply complete a chore.
An adult requires 2 units of food to prevent them from starving, two rounds of starving in a row, and you're dead! Adults also don't like eating 2 of the same type of food in a season, but sometimes they don't have a choice. Happiness is a score from -10 to 10. At positive levels the character can sacrifice some happiness to work even harder and gain a level in a chosen field. At negative levels, the player loses a level in every skill for each point below they go, to a maximum of 0. If there happiness reaches -10 they die from depression, however at the start of a new year a character instantly resets to 0 if in the negatives, after all they lived another year, and they should be happy and full of hope.
Serfs are the other residents of town, they can be hired by characters to do chores for them, and they'll work for food. Serfs being less then "noble" players, only require 1 unit of food a season to survive. Character's spouses and children are not serfs, even if they are not being controlled by a separate player. Serfs appear only when hired, but do not leave when fired, and become the baron's problem. Serfs cannot have professions, and the only jobs they can do are build (whether it's a structure or simply a garden/field/pasture).
Citizens are npc characters, they only appear when a need is met or needs to be met, they will offer services and products in exchange for money, but they will also pay other players for resources they might provide, like food, wheat, wool, ore, whatever. Citizens can also be taxed by the baron if he chooses, as can the players.
Other stuff, other stuff will be addressed when and if it becomes important. Such as marriage of children to serfs or other players. But for the most part the baron and possibly the players get to make most of the mechanical decisions of such things.
Game guide.