Welcome to iMore! No, you don't need to add contacts to any list. Maybe your favorites in the favorites section. But in the Facetime app, you just start typing a contacts name and it appears. They have to be iPhone or iPad users. You can also initiate a Facetime call from the contact's profile card in your contacts. For non contacts who use iOS, you'll need to enter their number in the FaceTime app.
Sent from my ancient but trustworthy iPhone 5.