We know, obviously, that the Earth is quite small in comparison with the size of the universe. Here is the best analogy I've come across.
Imagine you give a baseball to a five year old and ask him to throw it as far as he can. Say it goes 30 feet. Now, ask the best pitcher in the MLB to throw a ball as far as he can. Roughly the distance between the two can decently represent the difference between the Earth and the universe.