Simple

You just went to the Google home page.
Simple, isn't it?
What just actually happened?
Well, when you know a bit of about how browsers work, it's not quite that simple. You've just put into play HTTP, HTML, CSS, ECMAscript, and more. Those are actually such incredibly complex technologies that they'll make any engineer dizzy if they think about them too much, and such that no single company can deal with that entire complexity.