Normally when people think of yams it's in the context of the sweet stuff served at Thanksgiving. But a true yam comes from Africa, and it's a much larger root with a white flesh and a barky exterior.
As compared to their distant cousin the potato, yams have a lower glycemic index, so they help you stay fuller longer.
That, and they are a powerhouse of nutrients. They are high in vitamins C and B6, manganese, and dietary fiber. Also, since they are high in potassium and low in sodium, yams are said to protect against heart disease.
I usually give yams over to one of my chefs. He's one of the hardest working guys in the business: Chef Mike. He's very reliable, and you don't have to pay any health care for him.
In a conventional Chef Mike (home microwave), cook the yam for seven minutes or until it gets nice and soft.
Or, roast it traditionally in the oven. It will give the yam a distinct aroma that you don't get in the microwave.