Complex sentence: When they started attending Hollywood Professional School in 1964, they met up with Michael Lloyd, a pianist and guitarist who had been playing in several surf groups such as The New Dimensions with Jimmy Greenspoon later of Three Dog Night.
Split into simpler sentences: When they started attending Hollywood Professional School in 1964, they met up with Michael Lloyd. He was a pianist and guitarist who had been playing in several surf groups such as The New Dimensions with Jimmy Greenspoon later of Three Dog Night.