Uses for a stamp:

To put on an envelope as payment for delivery of that envelope.

*Ignore this one. The purposes for sending a letter vary, but I would also consider this a valid example. To send to a waiting missionary or service member. Or alternately to crush the hopes of said individual.

To stick two pieces of paper together at the ends, in case you need the two to come apart easily, but stay together for a short amount of time.

To pay off a bribe to an eccentric billionaire.

To entertain your baby for about 43 minutes. This a little expensive though.

To decorate a room i.e. wall paper. This is also a little cost prohibitive.

To proclaim a piece of government propaganda that can be conveyed in one square inch.

If enough are used, they could act as a mute on a drum.

Stamps are actually used in as a secret ingredient in Velveeta and other highly processed cheeses.

They can be used as the butt of a joke, like the one above.

They are the bearers of news that is neither urgent enough for a phone call, nor menial enough for an e-mail or text. Or in other words, they are rarely used for the purpose of message bearing in our society.