In 1686, what did sir issac newton explain with his three laws of motion?

He explained force and motion.

By explaining the laws, he described how force works when it affects a body and how the body is put into motion as a result of it. He explained numerous situations like that body in motion tends to stay in motion, or that when an object applies force on another object, there is a backlash and the object that inflicted motion has to get force back to it, and things like that.