There are three basic forms of advertising on other web sites: CPM, CPC, and sponsorships. We're going to cover each here and talk real quick about their upsides and downsides.
CPM Advertising on web sites
CPM is the abbreviation for Cost per One Thousand. In this case, it is cost per 1,000 ad impressions on a web site.
Let's say you were going to advertise on this web site and on this page particularly. Let's say we sold you advertising for a $10 CPM and in exchange you were able to run your banner on this page. Then let's say this page received 2,000 impressions per day. The total cost for you to advertise on this web page would be $20 a day.
CPM is pretty much the oldest form of advertising on the Internet. It's also now probably the least popular form of advertising on the Internet and is being replaced by CPA advertising. The reason CPM is no longer very popular is because of the decline in click through rates for web banners. The industry average is now just one quarter of one percent, or 1 click per 400 impressions. If you're paying a $10 CPM, that comes out to $4 per click - ouch!
However, if you can pick up cheap CPM advertising on targeted web sites (i.e. $1 - $3 CPM) it still may be worth it. It's something you'll have to check out.