On the home page of YouTube.com I find thumbnails of videos -- from featured clips to paid ads -- as well as a search box to enter text. Anyone can watch, although if you try to click on something YouTube deems "adult," it will ask you to register. (It's free, and a minor could easily give a fake birth year, making himself 18.)
My interest is piqued by a video named "Shaving My Eyebrows." The film launches in my browser: Eyebrow-guy discusses his fear of looking weird as he shaves his beard, head, and brows. The video is also surrounded by "related content," 1,200 videos posted by other users, from "Drunk Girl Shaving Her Eyebrows" to TV commentary on Britney Spears' bald-head episode.
I navigate the site by clicking from one linked video to another, or by "channel-surfing" (much like watching TV). Before I know it, the entire afternoon is gone -- and I've become an expert YouTube user.