Smart Card Program

Hello,

I'm developing a VB.NET program to manage the customers of a shop and I would like to implement a Smart Card system to memorize some informations about it, such as the money of customers

I've discovered in internet some tools about Smart Card and I started from this to understand how to read and write information on the Smart Card.

Now I'm very confused, because I don't know WHAT I have to memorize on the Smart Card and in which manner.