In using the LATCH method, lower anchors are used instead of the seat belt to install the car seat. If your vehicle has the LATCH system, there are anchors in the back seat where the cushions meet. There are also tether anchors located behind the seat. In sedans, they will be on the panel behind the seat. In most minivans, SUVs or hatchbacks, they will be located on the back of the seat, ceiling or on the floor. The child safety seat will have attachments that fasten to these anchors.
If you use your seat belt to install your car seat, check your owner's manual to see if you will need a locking clip to keep the belt locked into position. Most newer vehicles do not require a locking clip. First, fully extend the seat belt, then allow it to retract to keep right around the car seat. Some car seats will have a lock off built in that will lock the seat belt.