Iron the interfacing to the wrong side of the 5 X 16 1/2 piece of fabric that you want to be on the inside.
Line up the bottom edges of the folded piece and the piece with interfacing and then pin together. Starting over from the edge 1 1/4 inches sew lines parallel with the edge starting from the top of the crayon pocket, back-stitching at the top to reinforce. Sew the lines one inch apart across the pocket. You will have 1 1/4 inches on each side.
If you want to use ric rac, pin it around the edge as shown. Fold the ribbon in half and pin it on the edge. Note: On the one, I didn't use ric rac I did a blanket stitch around the edge when finished.
Pin the remaining piece of 5 X 16 1/2 inch fabric right sides together with the pocket piece. Sew around edges with 1/4 inch seam. Leave about 3 inches across the bottom for turning.
Trim corners, turn, press and topstitch being careful to catch all layers of the opening to close
TIP: A rotary cutter, ruler and mat make it really easy to cut out these pieces. I love this folding cutting mat that also serves as an ironing board. (affiliate links)