This is a test of muscular endurance. The idea here is not to go to failure with the descending rep scheme. The squats and lunges will burn your legs, the push ups your shoulders. The idea is to move steady and solid for your time under tension.
Scale the push ups with hand release if needed, and if your push ups break down, don't be afraid to scale them back as you go. One each side counts as one rep for the lunges (i.e first round is 10 left and 10 right).