Matt Might has diagrammed the PhD this way in his brilliant Illustrated Guide to the PhD. I love it because he cleverly shows that doctoral research pushes beyond the edges of what is known, to discover new knowledge outside the boundaries of the human record.
This is what examiners are looking for. In fact, they can't award the PhD unless you've demonstrated that you have made an original contribution to what is already known. You have to poke at the edge of human understanding and find your own Eureka! moment.
And that's hard. You're in unchartered territory. You find yourself the world's leading expert on a topic when previously you were only a student. It's daunting when you realize you've found out something that even your academic supervisor doesn't know. How do you tell people about what you've discovered?
Well, that's the purpose of a thesis: to describe your adventures into the unknown, to reveal what you found, interpret it for the reader, to show what it contributes, and suggest future research, based on your work.
Still not sure what exactly a PhD is? Take a look at all the steps that Matt explains, and then when you get it, give me a shout and we'll discuss.