Go on your profile and under your picture it says "Details" under that you'll see "Verification" click on about verification and from there it'll tell you what to do.
If you're not verified don't bid... As per Listia rules if you win an auction and your address isn't verified I can keep your credits and relist my auction. Go on Listia from a computer and scroll down to the very bottom of the page and click on "How it Works" and it'll give u all the info u need to know about Listia (rules, how to get verified, etc).