Buckwheat is a naturally gluten free pseudo-cereal, meaning its seeds are used like a grain but are botanically unrelated to wheat. The seed is the flowering part of the plant. Buckwheat is more related to plants like sorrel and rhubarb. Because of these traits, buckwheat does not contain any gluten. The plant itself is a short season crop that grows well in low fertility or acidic soil and doesn't require much fertilizer to grow. It is a wonderful cover crop after other crops have been removed. Buckwheat is an excellent pollinator which typically produces darker colored honey.
Buckwheat is a rich source of three B vitamins (riboflavin, niacin, pantothenic acid), high in fiber and even protein. Here is a link to the USDA Food Data Center. As previously mentioned, Buckwheat is naturally gluten free, but buckwheat flour products may have gluten contamination from production.
Buckwheat's culinary use is either as flour or groats. Buckwheat flour is popular as noodles or pancakes. You can find buckwheat flour or pancake mix available for sale. Groats are often created the same way most porridge are created.