YouTube's partner program places ads alongside original content and then splits the revenue with the creator. Michelle Phan is making thousands showing women how to apply makeup and Rob Homayoon is doing the same instructing on origami.
YouTube says 15,000 people are in their partner program and hundreds are making six figures a year. Thousands are making about a grand per month. It isn't likely you'll do that well, but then you'll never know unless you make a video and post.