I assume I have to give it emails of people I'm inviting. But I already have their emails in my address book - do I have to type them all in again?
In short, I don't understand what I have to do to accomplish anything, and at this initial point where I first visit your site, I don't care about the automatic confirmation/cancellation feature. It's the actual usage that I don't understand, and there's nothing there to describe it.
You need to focus more on the whole experience, not just a single feature.