Complex sentence: He started his writing career by writing short stories for children's on the topic of Umru ayyar and Taarzen a typical Urdu kids stories and he got much fame on it after that he started writing Imran Series and gradually become a pure writer of Imran Series.
Split into simpler sentences: He started his writing career by writing short stories for children's on the topic of Umru ayyar and Taarzen, typical Urdu children's stories. After that he started writing Imran Series and gradually become solely a writer of Imran Series.