I'm beginning to seriously doubt the OpenID community despite that fact that it works.

I'm in the process of currently evaluating OpenID as an authentication service for 'this' site and while the promises are great, I just can't get it to work. And I'm really lost.

I ask of the SO community to help me out here. Give me answers and show me examples so I can leverage this in the way it was meant to be.

My scenario is very typical. I want to authenticate users through a specific Google Apps domain. If you have access to this Google Apps domain, then you have access to my web application.

Where I get lost, is all the prerequisites and dependencies involved.

1. What is XRD?
2. What is Yadis?
3. Why do I need XRD and Yadis?
4. What do I need to do to deploy OpenID authentication on my website?

Also, this is really important to me.

When I login to SO, I use my Google Account. When I click the login button I'm presented with this confirmation page. Where I'm granting SO the right to use my Google Account credentials.

Somehow, Google knows that it's "Stackoverflow.com" that's asking me if it's okay to login. And I wish to know what manner of control I have over this little text. I intend to deploy OpenID on several different domains but I would prefer if they would all work without having to be individually configured with special parameters, such as secret API keys and what not. However, I don't know for sure if this is a prerequisite of OpenID, that or the Federated Login API that Google provides.