Complex sentence: Miyagi shows Daniel the secret to his family's karate--a handheld drum that twists back and forth illustrating the "drum technique", a block-and-defense karate move that Daniel begins to practice.
Split into simpler sentences: Miyagi shows Daniel the secret to his family's karate--a handheld drum that twists back and forth. This "drum technique" represents the block-and-defense that Daniel begins to practice.