Overlap style liners are installed under the top rail of the pool. To install an overlap style liner, the top rail of the pool is removed all the way around the pool. The liner is put in the pool, and draped over the top of the walls of the pool. Plastic coping strips go down over the liner and the top wall, holding the liner in place. The top rails are then put back on the pool, and the excess liner hanging down on the outside of the pool is trimmed off. If you have an overlap style liner, you can look under the top rail on the outside of the pool, and you will see the liner hanging down.
Above Ground Pool Beaded style liners have a groove, or lip, all the way around the top edge of the liner. This lip is snapped into a track that runs all the way around the inside of the pool, up at the very top of the pool wall under the top ledge. This track (bead receiver or coping) is what holds the liner in place, and you should be able to see the track if you look up under the top rail on the inside of the pool.