If you already have a website and you have traffic google's adsense can be a good way to make money. They put targeted ads on your page and pay you a certain amount (usually 5-20cents per click depending on the keywords) every time somebody clicks on one of the links. Search engine optimisation is a good way to provide more traffic to your website. Like Nicole said...your website must provide something valuable to the customers. This will keep a constant and increasing flow of traffic, and therefore more clicks...so more money.