If you know the basics of braiding, you can create cornrows. While braids or plaits hang freely from their individual sections, cornrows are braided to the scalp.
First, use the tail end of a rat-tail comb to create the size section you want. Skinnier sections will result in smaller cornrows, while larger sections will yield bigger cornrows. Here, a section is parted in front to create a cornrow directed to the side.