Gather a sheet of paper, scissors, and glue or tape
Place the paper flat with one side facing you
Fold the bottom edge up toward the center
Fold the top edge down toward the center so the edges overlap slightly
Tape or glue the overlapping edges to form a pocket
Fold the left side inward toward the center
Fold the right side inward toward the center so the sides meet or overlap
Seal the side flaps with tape or glue
Insert the letter into the pocket
Fold the top flap down to close the envelope
Tape or glue the top flap shut if needed