You use kefir grains to make cultured products, usually cultured milk. When you culture milk with kefir grains it turns out a bit like a yogurt drink but it has a different mix of beneficial bacteria than yogurt, so I find both kefir and yogurt helpful for my health. And unlike a yogurt starter, the grains will continue forever to culture your milk, and will even multiply like crazy, if they are cared for. Check out the kefir thread in this forum. It's usually on page 1 but now and again on page 2.