Matt Cutts: How Google handles robots.txt file?

In the video, Matt Cutts, explains how Google handles the robots.txt file? Why is my url showing up in Google when I blocked it in robots.txt? Did you fetch that url? How do I make that url disappear from Google?

In the video, Matt Cutts, explains how Google handles the robots.txt file? Why is my url showing up in Google when I blocked it in robots.txt? Did you fetch that url? How do I make that url disappear from Google?