There are a variety of gluten free grains available which you can enjoy in place of the forbidden wheat, rye and barley, if you have celiac or are gluten intolerant.
Some can be cooked and served with a meal as a side, such as rice, quinoa and millet. However, that is not the only way they can be used on a gluten free diet. They can be ground, or milled, and used in place of wheat flour in your cooking and baking.
When shopping for gf grains, I advise you to avoid the open bins in stores where you scoop the contents into a bag yourself. The risk of contamination is just too high! Stick to ready packaged ingredients, and remember to check the labels to keep yourself safe.
Eating gluten free can work out expensive, so you might like to consider investing in a grain mill. You can then buy the grains in their original form and either cook them "as is" or grind them yourself, which should save you money in the long run.