Web hosting + blog registration = confusion

I have a question today.  Does anyone out there use web hosting for their website?  Also, do you register your blog?  I’ve been doing research on these two topics and I’m still not understanding them completely.  Apparently a web host makes your website accessible on the world wide web.  This is strange.  The minute I created a domain name, I was accessible to everyone on the internet.  I’m not sure I get it.  Among providing accessibility though, hosting sites will provide you with various amounts of disk space to back up your content to.  Some hosting sites also provide security monitoring and advertising credits (which I’m still not quite sure what that is).  I don’t know about you but the back up services alone are enough reason for me to purchase services.  Does anyone know if Blogger does this already?  Back up your content?