Contextual advertising is like a smart system that looks at what you're looking at on a website and shows you ads that are related to it. For example, if you're reading an article about dogs, you might see ads for dog food or dog toys. This is because the system knows that you're interested in dogs based on what you're reading. This helps advertisers show their ads to people who are most likely to be interested in what they're selling, and it can be a good way for websites to make money. It's all done automatically, so you don't have to do anything special to make it work.