I don't want to book a flight yet, so can I use the booking widget to find out just how much a flight is going to cost?
 

Yes.

When you click the Next button, the next screen to come up has dates and the Book button.

Pushing the Book button doesn't mean that you will be booking a flight. It just takes you to the screen that has all the dates and times of flights.

Once you have found a suitable flight you can go on to book that flight or if you don't want to continue, just close the Air New Zealand window.

You can always come back later to book your flight.
 

I've found the flight I want to book. What do I do now?

Once you have chosen your flight(s), continue by using either your Airpoint Dollars or using normal payment methods like credit cards, debit cards or internet banking.