You should see an icon in your systray, like this:
That is what you should see normally but if not...
click start button on the bottom-left of the screen, hover over where it says "All Programs". A menu should slide to the right, and if you're up-to-date then just hover over where it says AVG 7.5. A smaller menu should appear then you just click on "AVG Control Center."
This should get it working if the AVG is properly installed and it's just a matter of the AVG not being started.