Using a Clay Bar

I just gave my daily driver Isuzu Rodeo it's bi-annual wash yesterday, followed with clay bar and wax. My wife asked what the clay bar was for, and I had her run her hand over the freshly washed fender. Then I had her run her hand over the hood that had already been clayed. NOW she understands! I use Meguiars Quik Detailer as the lubricant.