Flipping websites means, you buy a domain name, then put content on it to make it look like a site and then do little promotion to get in indexed and known a bit. After all this, you sell it. The idea behind this is, you invest some money in buying and domain name, putting content on it and promoting it, and then you sell it at higher price than your expenditure. This way making you profit. The amount of money you can make this way depends upon how good you are in choosing a "hot niche", how good are you in putting up "unique content" and how good you are in "promoting it a bit". This way you can turn your $30 investment into $300 too. Many people do it and earn this way. I remember I had given a free ebook on website flipping to on webmaster-money in some section.
Hope it helps!