This article contains information about using FaceTime that may help:
On iPad, iPod touch, and FaceTime for Mac, you need to add a person as a contact using the FaceTime or Contacts app before you can call them.
How do I make a FaceTime call?
You can make a FaceTime call in multiple ways, depending on your device:
iPad 2 or later, iPad mini, iPod touch (4th generation) or later, and FaceTime for Mac: You can place a FaceTime call using the following apps:
- FaceTime: Place a FaceTime call using your contacts list.
- Contacts: Tap the FaceTime icon to place a FaceTime call to the contact you are viewing.
Here's some info on how to add a contact: