If you are hip thrusting simply attach the weights to your belt by pulling the side straps through the belt's side loops, place it above your waist and thrust up. There is no need to use the back strap for hip thrusters. Naturally, the belt will form to your hips as they rise. This guarantees a snug,secure fit.
For all other movements: Attach the belt around your waste using the Velcro back strap. Then using the velcro side straps attach your prefered weight. This will allow you to do standing and walking movements without worrying about holding your weights in place.