Pull your hair back and measure (or visually estimate) the width and length of your face. If they're roughly equal, with the widest part at your cheeks and a soft jaw, you have a round face.
The goal for round face styling is creating the illusion of length and angles. Volume on top, minimal volume at the sides.
Angular frames with strong horizontal lines create contrast with soft round features, adding definition and perceived length.
Angular frames are the priority for round faces. Rectangular frames create the strongest contrast with soft curves.