Complex sentence: He began his career working as a contract actor for Desi Arnaz and Lucille Ball's Desilu Studios, becoming part of Lucille Ball's Desilu Workshop, in which Ball worked with and nurtured young performers such as Osborne and actress-singer Carole Cook.
Split into simpler sentences: He began his career working as a contract actor for Desi Arnaz and Lucille Ball's Desilu Studios. There, Osborne became part of Lucille Ball's Desilu Workshop, in which Ball worked with and nurtured young performers such as Osborne and actress-singer Carole Cook.