Complex sentence: The series "Billy's Boots" is about the boy "Billy Dane" who's isn't a very good football player until he finds a pair of old football boots that once belonged to the famous football player "Dead Shot Keen".
Split into simpler sentences: The series "Billy's Boots" is about the boy "Billy Dane" who's isn't a very good football player. But on some day, he finds a pair of old football boots that once belonged to the famous football player "Dead Shot Keen".