Cut your case piece to 7 3/4x 3 1/4
Score the paper at 3 1/8, 3 1/2, and 3 7/8
After scoring fold all score lines, then fold your paper on the 3 1/2 score line and take scissors and cut 2 slits up to the score line to fit pen.
-Note: the 3 1/8 side is the front of your holder
Take 2 pieces of sticky tape and place them on the inside score lines between the 3 1/2 and 3 7/8 score lines. Then fold over and hold down tell it is secure, that is what make the place for your pen to go. I get my small pens from staples. In my pictures I cut a 3 inch square to the front of the holder and any decoration is cut 2 or 2 1/2 inches.
I hope that makes sense and thanks for looking.