How do I find the airplay button, it's doesn't appear on my iPhone 4S?

Double click the round home button, the scroll the bottom to the right until you see a triangle partially in a square. You will need something like apple tv to use it tho.

If you dont have your apple tv and iphone on the same wifi and both on, then you will not see it until you have them both on and on same wifi.

This is how it works on my iPodtouch:

http://www.youtube.com/watch?v=u5RfCh6jpBM

Your welcome.