I always buy flights online. I shop around alot. Type in what you want eg: Sydney to Melbourne flights and you will get alot of pages come up.
Usually Jetstar or Virgin are the cheapest and Tiger.
They will email you your travel itinerary and receipt as soon as you have paid online.
You can also check in online before you leave. In some cases you can pick your seats while you book.
It is so much easier and cheaper, once you have done it once, there is no going back