These websites offer you to have your own page by signing up. You can customize their looks, add and remove functional modules, and customize the name of your page under their domain. These sites also offer premium paid services where you can optimize your usage of their site and add more customizations. If you happen to register for a free account, of course they wouldn't do it for charity purposes. They put ads on your page so they could earn from
you getting a free account from
them. Of course, when you upgrade your account, you wouldn't have to see these ads on your pages anymore.
