The key to making easy money online is the availability of a certain item only with you. If one product is available only with you then the people that want to buy that item has no option but to buy from you. This principle is the same in the real world and the virtual world because those people that want the product have no option but to buy from you.
Now what does this mean when we come to the online world? The easiest money you can make online is being as an affiliate. You register to some affiliate company where there are hundreds who want your participation very much. Clickbank and amazon are well known affiliate networks. After you signup for them you can sale any of the product you see there and get a percentage of the sale. The other way is you can create your own product and sell it online. But the easiest is being an affiliate.