General guidelines for installing child car seats include following the specific weight and height restrictions given in the seat's owners' manual. Also, follow the instructions in your car's manual, as many newer cars have a LATCH system designed for car seats, while older cars use the seat belt.
If a car is equipped with a LATCH system for child car seats, find the small metal brackets just inside the crack at the base of the car's rear seats. Carefully read and follow the instructions that come with the car seat to determine how to connect it to the LATCH system. Typically, you find long straps with large metal clips at the end. These are designed to hook onto the metal brackets in your car.
If your car does not have a LATCH system, you must use the adult seat belts to feed them through the car seat as shown in the seat's manual. After you buckle the seat belt, pull it tightly and try to lock it in place by giving the belt a quick tug near the top shoulder of the belt where it connects to the car. Many communities offer a child car seat check through the local fire department. They are trained to ensure that your child's car seat is properly installed.