Either you already have a web site, or are planning one. You have original content that others find valuable. How can you profit from providing this information to people? You could try charging people for it but a popular alternative is to accept advertising. This keeps the content free for your visitors, while providing you income.
The simplest way to accept advertising on your web site is to sign up with a service like Commission Junction. Through Commission Junction a web site publisher has access to hundreds of different advertisers, and can select from among them for adverts of interest to their web site visitors. All payments from the advertisers are conveniently collected into a single account, and paid by check or direct transfer into your bank account.
For example, let's say you have a web site about James Thurber. You join the Amazon.com affiliate program, and create links from your site to the books of James Thurber on Amazon.com. Now when a visitor to your web site follows those links and buys something from Amazon.com you are paid a 15% commission.