An OpenID provider is a web site you login into before you visit other OpenID enabled web sites.

The first time you visit an OpenID enabled web site you are redirected back to your OpenID provider, it will then ask you if you trust the site and whether you want to pass it some personal information which will save you typing into the new site, which you used to do. For example your name and email address etc. In many case you will choose to allow this information to go over to the new web site you are visiting, but for some you may choose not to do so.

On visiting the OpenID enabled web site for a second time if you have logged into your provider first, you will only have to enter your OpenID address, which looks just like a web address. EG http://markcross.openid.co.uk

Actually an OpenID address is an ordinary web address, but some simple code ebedded in the web page tells the OpenID enabled sites' who your OpenID provider is and how to speak to that web site.