When I registered both times (once a few years ago and once a few month ago) I didn't do the premium membership or wallet. I don't think you need to.

http://auctions.yahoo.co.jp/jp/show/entry_navi
You got as far as the above page right?

Once you've got a Yahoo ID, registered for the acutions, and confirmed your email address you should be able to bid. Make sure you are logged in and take a look at some auctions. Try bidding on a few to get used to it (try not to win or bid something up like crazy!).