What imthatguy is doing is affiliate marketing. Basically you try to sell someone else's product for lets say, $49.95. If a customer buys it from you, you get say $30.00. To make them sell you can put it on a website which is called a landing page. Now you usually want to start an ad campaign with google adwords. Those are the ads you see on right on a google search when you search for something. Someone clicks on the ad and goes to your landing page. Then someone buys it with your affiliate ID, you get $30.00 commission. Sell just 10 a day and thats $300. If you know what you are doing, and the product you are promoting doesn't suck, its easy to make money. I've heard of guys making $1000 a day in commission. Of course that is sales, not profit. The commission varies from product to product of course.
There is a lot more to it but thats the basics. I am just starting and I get $2500 a week average in sales. You may think its alot, but there are dudes who do $5000 in ONE day.
agatto2, do you currently use google adwords? How do you provide delivery of your product? I use e-junkie. They store your file and even emails the download link to your customer the instant they pay. You just sit there do nothing. Well almost nothing. They are integrated with google checkout and paypal among others too. All for $5 a month for 100mb of space. Check it out. E-junkie Shopping Cart for selling downloads & tangible goods  | 
