How to use facetime on my iPhone 5?

My sister and I got new iPhone 5's for Christmas but we don't know how to use facetime.
How do I call someone with facetime?
Every time I try calling my sister with facetime, I can only see my own face and not hers. So how do I get to see her face and not mine?

She has to turn on her camera too

It would help if she answered the call