Paying by credit card? The payment will be processed by PayPal Australia Pty Ltd.
PayPal will attempt to lure you into registering. Registering with PayPal is actually pretty handy if you are going to be shopping on the internet again in the future, as PayPal will remember all your details. So you won't need to keep typing them.
But if you decide NOT to register (which is fine of course!) you will need to click a special button. It's labeled "If you do not have a PayPal account then please click here". If you click there you can make a payment without registering. There's a picture below that shows what you will see and where you should click.
Please note that PayPal frequently redesign that screen, for some reason. I try to keep up with their changes but sometimes I get behind. So it might look a little different by now. But I think you'll be able to figure it out!