What are the steps to secure the car seat in my vehicle using a lap or lap/shoulder belt?

Place the car seat firmly against the back of a forward-facing vehicle seat, thread the seat belt through the appropriate path, buckle the vehicle belt, then tighten by pushing down hard in the middle of the car seat while pulling the belt tight. Perform a safety check by twisting and pulling the car seat front to back and left to right to ensure it is secure. (Page 22-23)