For this instruct able, you need
Glue or tape
1. If you are working with rectangular paper, you might wanna look at this photos above.
Fold the square paper diagonally. Fold it in half, and bring the two triangles at the edge to meet. Glue or tape this.
2. Now, hold the paper as if you want to put your message in it. Fold the first slit downwards and glue or tape it.
3. Put your message in your new home-made, no cost, envelope.