Brad-t from Harajuju has a guide to buying from Japan that explains everything.
http://harajuju.net/Topic-Buying-From-JapanShort version:
Make an account on a proxy service like Jauce(my preferred one) or FromJapan. You'll then have to link your paypal account to it and put in details like your residential address etc.
Input the auction web address on the search bar of the proxy service(the link I posted above) in order to view it through the proxy's website. The proxy's website tends to provide a translation feature of the auction webpage but you could also use google chrome to automatically translate it.
Before making a bid, you'll have to deposit some money into your account.
You can then place a bid on the auction using the proxy. It's recommended you place a bid around 7 min before the auction ends. Unlike ebay, any bids placed in the last 5 minutes tend to add an extra 5 minutes to the auction itself thereby giving your competitors more time to decide whether they want to continue bidding or not and the auction would end with whoever wants to pay the most. Placing a bid around the 7 minute mark would thus draw less attention to the auction if no one is watching it.
The proxy service will place the bid for you, receive the item in Japan then ship it forward to you.
Of course the proxy service hits you with a bunch of fees for this transaction. It usually tends to be a deposit fee(on top any paypal fees that might be incurred),a fee on the cost of the item itself if you successfully win it, the shipping fees and bank transfer fees(The Japanese wire money to bank accounts instead of using a service like Paypal) within Japan and international shipping fees. In my experience, Jauce does not mark down prices(for customs) but FromJapan can do that if you request them.
If your bid is unsuccessful, you can withdraw your money from the proxy(with a slight fee here as well). The proxy service should have a guide that explains the fees and what percentages they charge on each transactional service.
Edit: Oh also the measurements listed are usually in centimeters. Jauce's interface is much easier on the eyes and very easy to use but FromJapan has slightly lower proxy fees I think, a bunch of features such as the ability to "snipe an auction"(place a bid before the 5 min mark) plus they can lower the declared value of the item if you request them.