Pool liners for above-ground pools come in one solid piece, but you must cut holes in them to accommodate filter jets and the drain. Cut these holes after you've installed the liner in the pool but before you've added water so you can cut them in the proper places to avoid water leakage.
Install the liner in your above-ground pool and use your marker to mark on the bottom of the liner the drain's location.
Use your razor blade to carefully slice a hole along the marks you made in the previous step.
Begin filling the pool with water. When the water level is approximately 6 inches below the location of your skimmer, turn off the water.
Use your marker to mark out where the next set of holes need to be -- these will be for your skimmer and filter jets -- then carefully cut them out with your razor blade knife. Do not make the holes too large, as this can cause leakage.