Complex sentence: The 2017 Las Vegas shooting was a mass shooting at a concert in Las Vegas in 2017, where bllets were fired from Mandalay Bay (Las Vegas) into a crowd of the country music festival attendees.
Split into simpler sentences: The 2017 Las Vegas shooting was a mass shooting at a concert in Las Vegas in 2017. Bullets were fired from Mandalay Bay (Las Vegas) into a crowd of the country music festival attendees.