Stevia is a South American plant able to grow in a range of climates. It is valuable as a sugar substitute, since its leaves are almost 300 times as sweet as sugar. Stevia is also tolerant of many different types of soil, making it a fairly easy plant to grow.
Plant a stevia starter in rich, loose potting soil. The stevia can be started in a small pot or even a cup, provided it has holes poked in it to drain and a drip tray.
Give the stevia as much sunlight as possible. Stevia likes sunlight, so try to put it in a south or west-facing window.
Keep the soil damp by watering the stevia every day. It should not be drenched, but it should never go completely dry either. If the air in your house is dry, mist the stevia as well.
As the stevia grows, transplant it into a larger plant. An 8" wide pot should do.
When the stevia starts to flower, nip the buds back by cutting them off with scissors. Flowering will weaken the plant, slow its growth and possibly even cause it to die.
Harvest the leaves when you want to use them. You can either chop the leaves up fresh and use them, or dry them first. To dry the leaves, either hang them by a paperclip from a line or set them on a paper towel. Then, crush and powder them.