Purchase or cut a 1/4-inch piece of plywood to the dimensions you have chosen for your storyboard.
Add 1 inch to all sides of your storyboard measurement and cut a piece of felt to those dimensions.
Lay the felt on a hard surface and center the plywood on top of it. Using a marker, extend the edges of the plywood out to the ends of the fabric at each corner so that a square is drawn on each corner of the fabric. Cut the squares out along the lines.
Fold the sides of the fabric tightly over the edges of the plywood and nail or staple into place.
Draw or trace your visual aid designs onto the felt. Cut the shapes out. If you wish to embellish the felt shapes, for example making eyes for an animal, cut the embellishment out of felt and attach it to the shape with fabric glue.
Stand your flannel board up on an easel if you wish. The felt will naturally adhere to the flannel when you place the shapes on the board.