Passive safety — what protects you after the crash has already begun.
A properly fastened seat belt reduces the risk of serious injuries in a frontal crash by about 50 %. The driver is responsible for ensuring all passengers under 15 have their belt on. From age 15 each person is responsible for themselves.
Diagonal section over the shoulder, NOT across the neck. Lap section low over the hip bones, NOT across the abdomen. No slack; the belt should sit snugly against the body. Clothing should NOT be tucked under the belt.
In a rear-end collision the head snaps backward, the headrest stops the motion and protects the neck. Adjust it so the top edge is level with the top of your head (the crown), not the neck. A headrest set too low is essentially useless. It can even worsen the injury.
Steering wheel (driver's frontal), passenger dashboard (frontal), side-impact bolsters in doors and seats (ribs + hip), curtain airbags in the roof (head protection in side crash). A boot-floor airbag does NOT exist.
A rear-facing child seat must NEVER be placed in front of an active front airbag, the deploying airbag can cause life-threatening injuries to the child. If the child must sit in front: disable the airbag manually (check the car's manual) or move the seat to the back.