Imagine that you have a rope staked into the ground at one end. The other end is allowed to move freely. At this freely moving endpoint, imagine white chalk is spread on the grass. The chalk would draw out a circle. Each point on the white chalk circle is the same distance away from the center.
Another example: we have a campfire and campers gather around it. The fire itself is the center. The campers would be on the edge of the circle if they are the same distance away from the fire (eg: all of them 5 feet away from the fire).
