Why can't I find Messages on my Macbook Pro (OS X)?

Hi

I bought a Macbook Pro last year, and it's running OS X. Ive had a few friends talking to me about the Messages app, but I can't find it! Searching for it I don't have anything along the name of Messages. I have iChat, so I thought maybe I still had an older version but in the "About" tab it says OS X! Is this the Operating System it came with, or does it come with Mountain Lion? I thought when I bought the Macbook it was already updated to Mountain Lion, but I guess not!

Any ideas? I thought it was something that would have just come pre-installed or whatever, but is it something I need to download? If so, where do I download it from?

Thanks, Olivialeeee