To my understanding, it's a bit like reddit in how there are many subreddit-like "communities". It's also a bit like other social networks in how there are "Yeah!'s" that work similarly to "likes". And not only that, but there is an activity feed, so if you would rather just see posts from your friends you can do that! I guess it is also like that for people who would rather use a layout more like that of facebook's. And of course all of it is made child-safe(like everything else nintendo does online) by the Miiverse code of conduct and the "report abuse" button.
