To use FaceTime on an iPod touch, you’ll need a fourth-generation or newer iPod touch, an Apple ID, and a Wi-Fi connection.
Unlike the iPhone, the iPod touch doesn't have a phone number assigned to it. Instead, your Apple ID email address serves as your phone number. If someone places a FaceTime call to you, they'll use your Apple ID email address.
To get started, make sure FaceTime is enabled on your iPod touch and then register your Apple ID.