Complex sentence: The Oldsmobile Achieva was introduced for the 1992 model year and was a front-wheel drive, compact car based on the GM N-body platform which it also shared with its siblings the Pontiac Grand Am and Buick Skylark.
Split into simpler sentences: The Oldsmobile Achieva is a front-wheel drive compact car that was introduced by Oldsmobile for the 1992 model year. The Achieva was based on the GM N-body platform, which it also shared with its siblings the Pontiac Grand Am and Buick Skylark.