explain how keplers law verifies newtons law of gravitation when it applied to orbiting planets

You have it backwards.  Kepler came first.  He analyzed a lifetime of measurements and observations that described the motions of the planets as we see them move in the sky.  From these observations, he came up with a model of how the solar system could be organized, and he boiled a planet's motion down to three simple-looking laws.A century later, Newton proposed his law of universal gravitation, and showed that IF gravity works according to his law, THEN planets MUST move according to Kepler's laws.