Sweet potatoes are often mislabeled as "Yams." You won't often find real yams here in North America. See the differences here. If it's smooth with a creamy orange colour and can fit in your hand, it's a sweet potato!
What you need
Two large sweet potatoes
What to do
Peel and cube potatoes and onions. Put into a 9x13 baking dish. Drizzle with oil, sprinkle with thyme (or your herb of choice) and salt. Toss to coat evenly. Roast in a 400 degree oven for approximately 20 minutes, stirring halfway through cooking time. You want some good carmelization as it really brings out the flavour.
At this point you can serve as is, but sometimes I dump them into a bowl, add a scoop of butter and mash with a potato masher.