The image formed by any mirror is located either where the reflected light converges, or where the reflected light appears to diverge from.
A spherical mirror is simply a piece cut out of a reflective sphere. Its center of curvature, C, is the center of the sphere it was cut from. R, the mirror’s radius of curvature is the radius of the sphere. The focal point F (the point where parallel rays are focused) is located half the distance from the mirror to the center of curvature. The focal length, f, is:
focal length of a spherical mirror : f = R / 2