Lay down the felt, and then lay one of your fabric pieces on top of it, right side facing up.
Fold the elastic in half, and pin it to the middle of the right side of the fabric, with the loop facing in as shown in the picture.
Then lay the top piece of fabric down with the wrong side facing up. Pin all around the edges, marking a space at the top right corner where you won't be sewing. I use a horizontal needle between two vertical ones to mark this. This hole will help you turn it right side out later!