You will only need an 8.5" x 11" piece of paper.
Step 1: Write Your Letter
Write a letter to someone. Turn the paper over so that the writing is face up on the desk.
Step 2: Create a Crease
Fold the paper in half lengthwise so that corners 1&2 and 3&4 are touching.
Step 3: Fold the Corners
Unfold the paper and fold all four corners towards the center.
Step 4: Fold the Side Into the Center
Fold side A into the center crease.
Step 5: Fold the Other Side Into the Crease
Fold Side C into the center crease. It should look like the picture after this step is complete.
Step 6: Fold in the Pointed Ends
Fold the pointed ends towards the center. After this step, the paper should be shaped like a rectangle.
Step 7: Flip the Almost Envelope Over
Turn the paper over so the "heart side" (or the "flat" side) is facing up.
Step 8: Fold the Bottom Up
Fold side D towards the center. The end result of this step should look like the second picture.
Step 9: Fold the Top Over the Bottom
Fold Side A over side D.
Step 10: Tuck the Corners In
Tuck the corners of side A into the corners or "pockets" of Side D.