Couscous looks like a grain but actually it is a variety of small pasta. It is mostly made with just semolina and/or white flour.
Couscous can be found in Pasta Aisle of most grocery stores. You can also buy it online from stores like Amazon.
Couscous shown in picture is called Pearl Couscous or Israeli Couscous. It is famous for it's nutty texture. And used in casseroles, savoury salads and even in desserts.
How To cook Israeli Couscous: Heat 1 tbsp oil in a heavy bottom sauce pan. Add 1/2 cup couscous pearls and toast until slightly brown (1-2 minutes). Add 1/2 cup of boiling water/stock. Cover and let it stand for 12 minutes or until pearls are al-dente. Fluff with a fork. Use as desired.
Another form of couscous is all-purpose quick cooking couscous which has texture similar to coarse semolina or grits. It is called quick cooking Couscous because it needs very less time, about 4-5 minutes to get ready.
You can try these recipes with Couscous.