Choose a sheet of paper
Place the paper flat in a landscape position
Fold the bottom edge up about one-third of the way
Fold the top edge down to overlap the bottom fold slightly
Unfold both folds
Fold the left and right sides inward toward the center line
Unfold the side folds
Fold the bottom flap up along the first crease
Fold the top flap down over the bottom flap
Tape, glue, or seal the side edges
Insert the letter or card
Close the top flap