Complex sentence: He began the study of Kyokushin Karate as a student in high school at the headquarters (honbu) of Kyokushin Kaikan at Ikebukuro, Tokyo, where founder Masutatsu Ōyama taught.
Split into simpler sentences: He began the study of Kyokushin Karate as a student in high school. The headquarters (honbu) of Kyokushin Kaikan was at Ikebukuro, Tokyo, where founder Masutatsu Ōyama taught.