Face time does not use a number on the touch as it doesn't have one, it uses an email address. First off you need to have the person you are face timing in your contacts along with their email address. You also need to turn on face time on your device: Settings>Facetime>On
Once that is done, connect your touch to a wifi network, go to your contacts and you should have the 'facetime' button appear. Tap it and off you go!