Mayali
Click on the apple at the top left-about this mac-more info and it will tell you. Needs to by mid 2011 (early 2011 for Mac Book Pro) running OS X 10.8 or newer (a purchase not an update) to mirror, most other functions such as home share work on earlier macs fine.
If you have an older Mac and you want to mirror look at www.airparrot.com a third party app.
Jules