These pay-per-click ads appear on your blog. Every time somebody clicks on an ad (which is supposed to be about a subject related to your niche), you make a few cents or more. Small amounts each time, but it adds up. This is extremely hands-off. You just need to get a code from Google, place it on your website - and the ads will automatically appear on your blog. Google will only show ads that are relevant to your blog so it's a good experience for your visitors and maximizes the number of clicks you get, meaning more income.
The internet changes so fast that one year online equals about five years in the real world. But the principles of how to start and grow a successful online business haven't changed at all. If you're just starting a small business online, stick to this sequence. If you've been online awhile, do a quick review and see if there's a step you're neglecting, or never got around to doing in the first place. You can't go wrong with the basics.