I purchased 17inx23in paper from LCIpaper.com
#1 take 13x20in cardstock and cut two 6 3/8 x 20in strips of cardstock.
#2 Score the paper at 9 3/8in and 3in. These will be creases to make the cardstock easier to fold.
#3 Fold the cardstock at the scored areas.
#4 Glue the 3in folded part. I used a glue gun because scrapbooking tape was not as strong. The glue is tricky but you get used to it.
#5 Now score the last flap. I just line the ruler up and score a straight line so folding is easy.
AND NOW YOU ARE DONE!