Websites most commonly make money through various forms of advertisements. Other options are "paywalling" content or selling optional subscriptions that provide the user with more content or enhanced features.
The most common methods of advertising on a website are "cost per impression" or "pay per click." Cost-per-impression ads simply consist of displaying a banner or image advertisement, and the website is usually paid a fixed amount for every thousand unique visitors that the ad is seen by. Pay per click requires the website's visitors to actually click on the advertisement for the site to earn a fee. A related form is affiliate marketing, which requires the visitor to not only click on the advertisement but to also make a purchase, for which the referring website is paid a commission on the total sale amount.
Various forms of paid memberships may also be sold. Sites may lock some or all of their content off from those who are not subscribers. This practice is commonly called a "paywall." The New York Times has become a high-profile example of a paywall site, and a number of other newspapers also employ the practice for at least some of their content.
Some sites also collect data on their users and then sell it to marketing companies.