A Basic Farm is used to grow vegetables from the seeds found all over the world. Once the seeds are planted, they will slowly grow into a plant which can be picked. After that has happened, a new seed can be planted. Manure, Guano and rotted food can be used to seed up the growth of the plant. After 20 plants have grown, the farm itself will have to be fertilized before it can grow more food.
While farms can be a good way of getting food without racking up naughty points from killing harmless animals (thus spawning a Krampus), it is also one of the least efficient methods of collecting food. It takes 40 daylight hours for the seed to grow which means it will be at least two days with no fertilizer even during the summer. This will produce only a single edible item. Further, all growing halts during the winter making this completely useless for 15 out of every 35 days.
What's the benefit, you ask? Well, if you have a Birdcage then you can feed the bird various vegetables to get seeds that will grow only that type of food. This is still rather laborious because the bird can at most produce 2 type specific seeds and one extra unspecified seed. However, it can be worth your while for some of the more beneficial plants such as Eggplant and Pumpkins.