Although potatoes do set seed, they do not grow true to seed. To get the variety of potato you want, you need to grow them vegetatively, meaning you re-plant a part of the actual potato. These pieces of potato are referred to as seed potatoes. Certified seed potatoes are certified by some government authority to be disease free. However, even certified potatoes can contract disease once planted, especially diseases that are not apparent in the seed stage like ring rot or fusarium wilt. Still, at least you have a bit of an edge, with some disease tolerance. You do not need to plant a whole, intact potato. Seed potatoes can be cut into pieces, as long as the pieces have at least 1 eye each. Keep reading the tutorial in the source.