Q: Where is FaceTime icon on iPhone 4s

There is no FT icone on the iPhone.  It's accessed via contacts.

http://support.apple.com/kb/HT4319

The iPhone does not have an individual icon for Facetime like the iPod. You access Facetime from you contacts. Open the contact you want to Facetime and there is a button on the page to connect.

There isn't a FaceTime icon.

Take a look at this Apple doc -> iOS: Using FaceTime

How do I make a FaceTime call?

You can make a FaceTime call in multiple ways, depending on your device:

iPhone 4 or later:  You can place a FaceTime call using the following apps:

• Phone:  While on a phone call, you can tap the FaceTime icon to invite the other party to a FaceTime call.
• Contacts:  Tap the FaceTime icon to place a FaceTime call to the contact you are viewing.