What's the point of the Swagbucks codes? How on earth do I use them?

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Okay, so I just created an account on Swagbucks since everyone seems to say it's good, and it does indeed look so. However, I went to visit the blog and suddenly saw all these posts about code hints. What I didn't understand is even if I figured them out, how do I use them? Where do I enter them? I didn't see on the site or the blog where to put them in, though I didn't dig all that deep either. Still, it should've had something in the FAQ or something like that. All I gathered is something about putting it in zendoo.com in all caps, but I don't know if you go directly to the site and it somehow knows you searched it if you're logged in or if there is somehow a way to find that site through the Swagbucks site or whatever. I may sound like a complete dolt right now, but I am brand new to the site and just learning the tricks of the trade. Someone please help!