First of all it’s incorrect to say they can’t control what appears. The person who owns the website simply goes under his control panel and can say what and what isn’t to appear on his website. After all if you run a pro-Nazi website you wouldn’t want ads for your local temple on it. 
But you can control it.
You CAN make money, but few people do. You are lucky if you can make enough in a year to recoup the cost of your website hosting fee.
You can get the same information in the “Google Ads for Dummies” book. Other search engines work similar but not the exact same.
I’ll oversimplify it a bit to explain.
You have a website, you sign up to put ads on your site. Google has a list of rules you MUST obey. (Like you can’t direct people to click on your ads. They have to do it 'cause they see the ad, not because you wrote “Please click on my ad.”
The people taking the ad out bid on “keywords.” The second bidder sets the price.
Let’s say the key word is “Cecil”
John bids $1.00
Joe bids $0.20
Because this is the SD the word “Cecil” appears and the John’s ad appears on TOP and Joe’s ad appears 2nd. John pays like $0.21, NOT $1.00. John is only charged if the person clicks on his ad.
Now most people click the top ad first, but as you can see, if you’re second from top, you may get enough clicks by bidding less and being second.
Now in the above example, Google charges John 21¢ because someone clicked on his ad. But YOU only get a small fracting, for hosting that ad. You may get say 2¢, while Google keeps 19¢ (of the total 21¢)
Google never tells you the exact way it calculates what you get. This is often critisized. But Google say, “Don’t like it, use another service”
They way to make big bucks is find a word that is holds a big bid. Obscure words are usually worth nothing, 'cause no one bids on them. Remember even if you bid $100 a word it’s the SECOND bidder that sets the price. If you bid $100 and the second bidder bids 2¢. You’ll only be charged 3¢, despite bidding $100
So if you find a word like “Computer Fix” (words can also be phrases) that may command bids in the hundreds of dollars and a click on a phrase like that may pay $100.00 a click, of which Google may give you $2.00 for hosting the ad. As you can see if you get 10,000 readers of your, say blog, that $2.00 ads up fast
Now I’ve oversimplified this a bit, as there are many other rules and scenerios to deal with, but BASICALLY, that is the idea. Other serach engines, like Yahoo, ASK and the like have their own rules.
You don’t need to pay to figure this out. Go to Google Adwords and look at their rules. Figure out which word will command a lot of money, if people click on it. Then find a way to create a website about that word, that will cause an ad with that keyword to appear on it. Then figure out a way to get tens of thousands of visitors a day to your site.
See it’s easy huh?
