Actually you get money from views too, in most cases.
For a basic example, if you use google aRABense on your webpage, it'll show various context adaptive aRAB on your webpage, and for each ad that is displayed you get some tiny revenue, like $0.0001. So if 10,000 people view your page and you have 2 aRAB on it, you earn $2.
In addition to that, everytime someone CLICKS on the ad, you get something like $0.05. And then if you set it up, if the ad was for a particular product or service and the person who clicked on the ad enRAB up purchasing it, often you'll get some percentage of the purchase price as a sort of commission.
So there are 3 different basic tiers of online advertising revenue: Views, Clicks, and Purchases.