First, read the English article below.

Run the sweet potato under cool tap water. Wash the surface of the sweet potato. Make sure to remove any dirt or debris stuck to the sweet potato's skin. Choose a pot big enough to cover all your sweet potatoes with water. You also need a pot with a lid. Fill the pot with water until the sweet potatoes are covered in water. Place the pot over on the stove and cover it with a lid. Keep the pot over high heat for 10 minutes. Then, remove the lid and take a knife. Use the knife to make a small puncture mark on the sweet potato. Once you've punctured your sweet potato, cover the pot again. Allow the sweet potato to cook for an additional 20 minutes over high heat. When it's tender, you should be able to place a knife through the sweet potato without meeting any resistance. You may have to cook a sweet potato slightly longer if it's not done after 20 minutes. Use a colander to pour the hot water out of the pot. Allow the sweet potato to sit in the colander until it's cool to the touch. If you need to cool a sweet potato faster, you can place it under cool running water. After the boiling process is over, a sweet potato's skin should slip off easily. Use a pairing knife to make an initial slice into a sweet potato's skin. From there, you can simply peel off the skin as if you were peeling the skin of a banana. 

Now, please write a short abstract for it in Vietnamese. Abstract:
Rửa khoai lang. Cho khoai vào nồi. Dùng dao đâm vào khoai lang sau khi đã luộc được 10 phút. Luộc thêm 20 phút nữa. Đổ nước ra. Bóc vỏ khoai.