A tangent intersects a circle in exactly one point. When two segments are drawn tangent to a circle from the same point outside the circle, the segments are congruent. The extension problem of this topic is a belt and gear problem which asks for the length of belt required to fit around two gears. Topics related to circle radii include inscribed circles and radii to tangents.
When we're talking about tangents, if I pick the point a and I drew a point of tangency or a ray of tangency ac from point a and if I drew another point picked another point of tangency b, and drew a ray through that, something special happens this segment between the point of tangency b and the point outside the circle a is going to be congruent to the distance between a and c so if you ever pick a point outside of a circle, and you draw two tangents to that circle you're creating 2 congruent segments.