The main components of a stamp:
1. Image
2. Perforations
3. Denomination
4. Country name

"Inverted Jenny", a very rare and expensive U.S. stamp, 1918

Postage stamps are pieces of paper which signal that payment has been made for the item to be mailed.

These days they have adhesive on the back. They are put on the top right-hand corner of an envelope. They pay the fee for having the postal service take the envelope to where it is being sent.