How to get FaceTime on my iPhone 4?

I have got an iPhone 4 and I can receive FaceTime calls but I can't make them because there's nothing to press? How do I make calls?

I think you go on contact and click on a number and you get an option

It asks you if you want to accept or decline.

Go on a contact and it should be an option to facetime if they have an iPhone, just click that and you should be able to call someone through facetime