He actually predicted the shape of the earth as" oblate spheroid", and his discoveries are many some of them are as follows , three laws of motion
1st law : Law of inertia that is ,an object in rest continues to be in rest unless it is acted upon by some force and a moving object would continue to move unless it is stopped by some force .
2nd law :The second law states that acceleration is produced when a force acts on a mass.
3rd law :For every action there is an equal and opposite reaction .
Universal gravitation was one of his famous discovery .
And as well he also discovered optics .Hope this helps :)