Doing a trial pad is highly recommended as you may want to modify for size and shape to suit your own needs. This provides the access to insert the liner. If you don't do this the pads end up with little bunches of material at each corner. This is necessary as it helps the pad keep its shape . Also note the black dots are about where the snaps should go.
Press snaps on the pad pocket.
Cut the liner size required . Regular are about 22 inches by 7 inches, mini are about 10 by 7. Serge around it. Fold it up and insert in the pocket. Care and Washing Wash your pads before their first use - this increases absorbency.