The Polar Coordinate System describes points in space using a radius and angle relative to the origin. Angles are measured using radians, where a full rotation around the circle is equal to the circle constant (tau) where radians. By convention angles are measured from what is considered the positive direction in the cartesian-coordinate-system with the positive angle direction as counter-clockwise.
A point is denoted with two variables: which represents the radius corresponding to the point and which represents the angle corresponding to the point. The interactive below demonstrates some example points in the coordiante system.