What is booster mode setup like?

In booster mode for children weighing between 40–120 lb and between 40-57 inches tall, place the child upright in the installation. Adjust headrest to be slightly above shoulders (at least one centimeter). Fit shoulder belt diagonally over car seat shell guide behind headrest and use lap-shoulder system only without adjustable bottom or anti-rebound bar. Seat must fit tightly so harness can be removed for booster usage. (Page 54-59)