Smart cards are used for a variety of purposes, including:

To use a smart card, either to pull information from it or add data to it, you need a smart card reader, a small device into which you insert the smart card.

Smart Card Resource Center
Hosted by Amerkore International, this site provides smart card news, tips, articles, free software, several FAQs, and resource links.

Smartcard and illustration - article
Byte Magazine article (June 1997) on the use of smartcards as a certificate solution. It highlights the iButton product from Dallas Semiconductor and contains a link to an illustration showing how smartcards work.

Yahoo!'s smart card companies page
Yahoo!'s directory of smart card companies.