Cowrie shells can be found in the Indian Ocean, and due to their sturdiness, among other factors, they quickly became one of the main means of payment in the ancient world, particularly in Asia, Africa and Oceania.
Cowrie shells are symbolically related to the female principle and the ocean, and they are supposed to bring with them protection by sea spirits.
Cowrie shells became an important tool in divination practices in Africa, India, Cuba and Brazil. Each culture uses them in its own way.
We normally ask a question before casting the shells, and the number of shells varies across cultures.