Why won't my Apple AirPlay & Mirroring work?

I have a Macbook Pro that I bought in July of 2011 and when I look up the specs, it states that my Macbook is a Late 2011. I bought my Apple TV in May and I believe it is a 2nd or 3rd generation, which should allow the Mirroring feature. My AirPlay is turned on, but there is no button in the menu bar for me to click and nothing is happening. Everything on my computer and Apple TV is up to date.

How can I use the Mirroring feature? If I can't, what can I do to play content with AirPlay?