Windows CardSpace is client software that enables users to provide their digital identity to online services in a simple, secure and trusted way. It is what is known as an identity selector: when a user needs to authenticate to a web site or a web service, CardSpace pops up a special security-hardened UI with a set of "information cards" for the user to choose from. Each card has some identity data associated with it - though this is not actually stored in the card - that has either been given to the user by an identity provider such as their bank, employer or government or created by the user themselves (see also "Introducing Windows CardSpace" on MSDN)
Using CardSpace with Windows Live means you don't use a password to sign-in to websites which accept Live ID credentials; Instead, just send your CardSpace card to Live ID to identify you: try it now!
Here a great webcast and step-by-step instructions on how to associate a personal card with your LiveID account.