You can find Seeds by breaking grass or by harvesting Wheat growing in villages. If you don’t want to farm Wheat and just want to see how to make Bread, see the next section.
Farmland needs to be within four blocks of water to be considered irrigated. There are lots of creative ways to build your farm to maximize land-to-water and get the most crops. See How to Farm Crops in Minecraft for some tips. Make sure to create your Farmland blocks outside so that the Wheat gets enough light.