Reserve from BtSSB/AAtP?

Hello, I live in the US and I would like to reserve a dress from AAtP's new set. I haven't ordered from them before, and I was wondering if there's someone who has done it before who can tell me the easiest way to do it. I looked on their site, and it appears you just use their online shopping cart, but its description of making payments is odd and a little vague. Thanks :)