There are several versions that you can review here.
I cut out two pieces from different patterns.
Outside material - 5 1/2" x 6 1/2"
Lining - 5 1/2" x 7 1/2"
(Note: The video below suggests a larger size)
Sew together on the 5 1/2" sides
Turn right side out (lining will show on the sides).
Press with an iron
Fold edges toward the center
Sew the short ends
Note: you can buy the tissue inserts at the dollar store or DollarTree but they will be a little smaller than the usual size pocket tissues.