Placing an Oats in the crafting grid gives you a Oats Seed.
To farm the Oats, you plant and grow the seeds (or the Oats itself) on tilled soil, once they're fully grown you can right-click them, harvest the Oats and let them grow again. When harvested by right-click, the plant doesn't break, and yields 1-2 Oats.
Shapeless Crafting Edit
Here are all the recipes using Oats: