Certified GKH Gardening Expert
There are a number of methods. The easiest is to take the tip of an existing plant, and place it in moist soil. It will root itself, and produce a plant from there. Otherwise, you can leave a sweet potato out in some light until you notice slips growing out. Take one of these, and let it root into soil.
This article will help you to grow sweet potatoes: https://www.gardeningknowhow.com/edible/vegetables/sweet-potato/grow-sweet-potatoes.htm