Affiliate sites are sites whose purpose is to drive traffic to merchant sites, and then get rewarded by the merchants for the customers they sent the merchant's way. The ways to drive traffic to a merchant are many - you can put up their ads, or give reviews of their products, or do some SEO stuff which I don't really understand so I can't tell you much about :) but typing 'affiliate site' or 'affiliate marketing' into google gives lots and lots of hits.
this might give you some interesting information too - it seems to lay out the requirements in nice clear steps (make sure you read all the way down the page :). the key is to have a site that looks good (i.e. professional/ trustworthy) and to make sure it is full of original content to attract traffic........
maybe you could do it in blog form sort of, with some of the entries talking about specific products? http://www.dooce.com has a category called 'daily style' where she puts up a product she likes for some reason, along with a link to where you can find it.... it's a brilliant format in my mind because it doesn't feel like advertising the product is her purpose - she's just writing about stuff she likes. And she's supporting her whole family with that site so she's bound to be doing something right......... :D
Almost forgot to mention - if you want to have a site search thing, you'll need a database, meaning PHP and stuff. You know how to do that?
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