▶ SUBSCRIBE TO HAPPY LEARNING! http://bit.ly/HappyLearningTV Educational Videos and songs for Kids. A polygon is formed by a closed polygonal line and the space inside it. To understand what that means, watch this straight line become a polygonal line as it forms several sides which eventually close. And what do you see? A polygon... Easy, right? A polygon is made of several elements... The side is each one of the segments that form the polygon... The vertex is the point where two sides meet