Q: How do I connect my MAC laptop to my Apple TV using airplay when the airplay icon does not appear at the top of my laptop?

I am new to the Apple world and I'm learning the ropes in a way. I have an Apple TV and a Mac laptop. I don't know how to tell you what it is that I have but its a 17" MacBook Pro that I recently purchased on craigslist. My wife has a Mac laptop of her own and being connected through the same network, hers has the airplay icon appear on its own but mine does not. Is this a setting that I need to manual activate and if so, how do I get to it? Any help would be greatly appreciated and thank you.