Dear Student,
The radius of curvature of a spherical mirror is the radius of the surface from which the mirror is carved out.
Now focus is the point where all the light rays meet after reflection if they were initially parallel to pricipal axis ( or light rays appear to be coming from focus in case of convex mirros). The distance between the pole and the focus point is known as focal length of the lens.
The focal length and radius of curvature are related by
Regards,