Remember when you were small, or at least smaller than you are now, and you wrote on your books something like;
This book is the property of
Sally Walker,
31 Spicer Street
Queensland, Australia,
the World,
The Solar System,
The Milky Way,
The Universe?

Without knowing it, you had used a system to organise your world.
Astronomers still classify objects in the sky in pretty much the same way.
Use the links below to explore further.

The Universe (including the Big Bang Theory)
Stars and Solar Systems
Our Solar System
The Earth