Ad question...if anyone knows

Hey all!

I’m just curious on how do most of these web galleries get those banner ads (or square ads) on their sites? IE, like Stylegala, [URL=“http://www.cssbeauty.com/”]CSSBeauty, or [URL=“http://www.unmatchedstyle.com/advertise/”]Unmatched Style. All of these sites have “advertising” pages, so I assume some of the banner ads actually go directly to the maintainer of each site to put their ads up.

Then there’s also sites like this: I Hear Blogs. I think those smaller graphic ads are just affiliate marketing?

Can anyone like give me a short primer on how these sites go about getting these ads? I’m assuming the first step is to have a good amount of traffic?

Thanks,
Eric Huang