Building a farm in Minecraft involves several steps:

1. 
   Select a location for your farm. It should be flat, open land with easy access to water.
   
2. 
   Prepare the soil by removing any grass, weeds, or other unwanted blocks.
   
3. 
   Create a perimeter for your farm by placing wooden planks or other blocks around the edges.
   
4. 
   Decide what type of farm you want to build, such as a wheat farm, a pumpkin farm, or a sugar cane farm.
   
5. 
   For a wheat farm, plant wheat seeds on the prepared soil. Wheat can be harvested by breaking the fully grown crop with a hoe.
   
6. 
   For a pumpkin or melon farm, plant the seeds and wait for the stem to grow. Once the stem has grown, the pumpkin or melon will appear on the vine.
   
7. 
   For a sugar cane farm, place sugar cane on the prepared soil next to water. The sugar cane will grow taller each time it is harvested.
   
8. Finally, build a shelter or a small house near your farm to protect yourself from mobs at night.

These are just a few examples of the many different types of farms that can be built in Minecraft. Some other popular farm types include:

• Carrot and Potato farm
• Bamboo farm
• Nether wart farm
• Fish farm (using different types of fish)

It's important to note that some farms need specific conditions to grow like a light level, temperature, etc. Also, keep in mind that some farms require more resources and time to build and maintain, but they provide more resources and experience as well.