The Isofix fittings are located in the rear seats of the car. These are metal fittings in which the child car seat is "attached" and allow for easy, quick, and secure installation of the seat in the vehicle.
The Top Tether is an additional attachment strap on the top or back of the seat, which holds it in place and reduces forward displacement of the seat during a frontal collision, providing additional safety in the event of an accident.