What are the proper steps to secure my child in the car seat with the built-in harness?

Place your child in the car seat with their back flat against the back, place harness straps over their shoulders and insert tongues into the buckle, verify straps are not twisted and securely latched, pull the adjustment strap to tighten, fasten the harness clip at the middle of the child's chest level with armpits, and ensure straps are flat and tight. (Page 26-27)