I update my Iphone 4s with IOS 6 but I m not able to use facetime even facetime icon is not available on my setting menu?

Did your 4S have Facetime on it before you updated? The 4S, new, shipped with Facetime and didn't need and update to iOS 6 to get it. However, if you purchased an iPhone that was designated to be sold in UAE, Saudi Arabia and a couple of other Middle Eastern countries, then the device does not have FaceTime and it can't be added.