Complex sentence: Still at school, he began to perform as a singer in a group called Bob Andrews and the Questors in 1961, switching to another group, the Whirlwinds, in 1963, and in 1964 formed a comedy double act called Pee & Knutt.
Split into simpler sentences: Still at school, he began his career as a performer singing in a group called Bob Andrews and the Questors in 1961. He then moved on to another group, the Whirlwinds, in 1963, and in 1964 formed a comedy double act called Pee & Knutt.