To this point, LeBron James has not really made any important contributions to society other than by providing entertainment.
LeBron James is, of course, a basketball player. He is not someone who is (at this point in his life) going to contribute greatly to society by curing diseases or enacting important laws. Like many athletes, James has a foundation that he uses partly as a means of doing charitable work. This, of course, contributes to society in a small way.
Of course, it is important for people to be entertained and James does contribute in that way. This is surely his greatest contribution--through his play he helps to entertain people, which is important because people need entertainment to help them stay emotionally healthy.