How does a card talk to the outside world?
A card needs to be inserted in a card reader (also called card acceptance device, or CAD). If the card is a contact less card, it just needs to be close enough from the reader for a fixed period of time.
The card reader always initiates communication. It provides power and clock to the card. First, it will usually select a card application using a special command called SELECT. Then, it sends a command to the application, which processes it and answers. The reader sends the next command, and so on. Simple, huh?