I'll tell you what. One simple click on an affiliate ad can earn you money. Yes, it could just be a few pennies but it could also be several hundred dollars. And that could be repeated over and over again.
Affiliate marketing is one of the least understood and yet, one of the best ways to make money online. What the marketer does is join affiliate programs, such as Clickbank, that have products or services they want to promote. The marketer promotes the product, finds customers for the company they are promoting and, when the customer buys, the marketer gets a commission.
The most common business model is the marketer creating a site (or sites) on topic(s) that are of interest to them. Once the site is established, and getting a large amount of targeted traffic, the potential for making a nice income can be as simple as putting up Google AdSense ads and/or a few affiliate links.
The Internet provides available traffic 24/7/365. The term 'business hours' has become meaningless. And the more unique the content, the greater the potential for targeted traffic. And the greater the targeted traffic, the higher the potential for earning income. And this traffic can come any time of the day or night, while you are sleeping or while you are on vacation. What a nice way to earn extra income!
There are many affiliate networks available to marketers. The key is to pick a topic for a site that is of interest to you. That way you will be able to keep it updated with good content. Good content will get you the traffic. And traffic will get you the sales.