To earn here at HubPages you need to sign up for google adsense and the other affiliate programs. Once you have done this you need to get plenty of visitors from search engines to your pages. Here's some info for beginners: http://hubpages.com/community/How-to-Make-Money-on...
Duplicate means that there is another copy of the work you published here, elsewhere on the web. If you have copied your own work here, that's ok but your hubscore for those articles will be penalized. HubPages wants unique content, not copied content. Copying other people's work is a big no-no. Hubs can also be flagged as duplicate if you have quoted large sections of text from elsewhere - such as The Bible.
More info here on the duplicate flag here: http://hubpages.com/faq/#duplicate_content