Complex sentence: Good Entertainment (official name: Good Entertainment Media Group, also known as Good! Enter) was a record label owned by CJ Music that was formed April 2003; they produced the popular boy band Shinhwa (after the band left SM Entertainment).
Split into simpler sentences: Good Entertainment (official name: Good Entertainment Media Group. Also known as Good! Enter) is a record label owned by CJ Music that was formed April 2003. Most notably, they were the producer of popular boy band Shinhwa (after the band left SM Entertainment).