The Farmer is the backbone of your food production. The farmer will cultivate the crops you assign him/her through the "Field" block (Scarecrow).
To begin with you have to craft the "Farmer's Hut" block in the crafting table and use your Buiding Tool to place the building. Once you "commit" to the placement of the farmer's hut, the block will be placed and the farmer will be automatically assigned (or you can manually assign one with the best "Traits" for farmer if you changed this in the setting tab in the Town Hall's GUI.
Best Traits are: Endurance and Charisma.
You now officially have a "Farmer!" CONGRATULATIONS!
Now you will have to issue the builder the "Build" assignment so he can build the "Farmer's Hut". He will be asking for the materials he/she needs. Make sure to check the "chat" regularly to see what materials the builder is requesting for any build/upgrade.
Once the builder is done, you will have to determine where your farm plot(s) will be located. Before the farmer can start, you will have to give the farmer a hoe, the crop you want to cultivate so the farmer can plant, and craft the "Field" block (Scarecrow). Place the "Field" block in the plot of farm land you want the farmer to work on and right click on it to acces it's GUI. Here you will place the crop you want for this specific field to be cultivated. The crops he currently cultivates are: Wheat, carrots, potatoes, beets and most "modded" crops (from other mods) as long as they have normal growth behaviour (Minecraft melons, pumpkins and sugarcanes are being worked on at the moment).
Note: the farmer will only till and cultivate crops that are (up to) 5 blocks from the field block. The farm land can be delimited by placing solid blocks (non tillable; sand, cobblestone, wood, etc) or air blocks in the ground next to the tillable blocks. This will cause the farmer to stop cultivating the land at this point, even if there is still tilled and/or tillable land after that solid/air block. Plan accordingly and create your plot(s) any shape and form you want taking into account that for each farm plot, the farmer will only work up to 5 blocks from the field block.
If you decide later to change the type of crop you want cultivated in that specific farm plot, just go into the "Field's" GUI and switch the crop there. Remember that for the dirt to be tillable and hold crops, it must have a water source to keep it tilled and crops stay planted (Minecraft limits the water source to permeate up to 4 blocks from it's placement).
- IMPORTANT: The farmer will take care of up to 3 "Fields", depending on the level of the "Farmer's Hut". If the Hut is only level 1, the farmer can only take care of 1 Field. Level 2 Hut then 2 Fields. Level 3 Hut (and up) all 3 Fields.
These are just some examples of what a farm plot can be like. you can be creative and make them any shape you like.
- Hint: If you see the builder has not finished building/upgrading your farmer's hut and you don't see the builder asking for any materials, go to the builder's hut and "recall" the builder and wait a bit to see what the builder needs. Watch the Minecraft "chat" section. Also you can go to page 2 of the builder's hut GUI and check the list of materials required, any material in the list that is still missing will be in red colored letters.
Now you can access the Farmer's Hut block (right click on it) and you will see a GUI with different options: