The following factors frequently contribute to a page be defined as supplemental in Google eye's.

Duplicate pages,
Identical title tags and identical description meta tags,
Not enough indexable content,
Website templates with large amounts of identical content per page,
Too many parameters in your URLs,
Actual (indexable) page content buried too deep beneath navigational elements.

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Domainmonster.com Customer Support Team.
Domain Name Registration Information & Resources.

How do i know if my site or pages have been set as supplemental in Google???

Please could you give me more infomation, how does this effect my results?

If you have pages like this, Google can mark you down and it can result in lower rankings. I think you can check whether your site has been blacklisted in the Google webmaster centre.