Complex sentence: It premiered at the 70th Cannes Film Festival in the main competition section, where Lynne Ramsay won the Best Screenplay award and Joaquin Phoenix won the award for Best Actor.
Split into simpler sentences: It premiered at the 70th Cannes Film Festival in the main competition section. At Cannes, Lynne Ramsay won the Best Screenplay award and Joaquin Phoenix won the award for Best Actor.