How to make theme demos quickly ?

Hi, I want to make some demos to demonstrate my WordPress theme? Can you tell me the quickly way to do that?
For pages like left sidebar/right sidebar/without sidebar . Need I make three different pages to demonstrate them or is there some fast way? I saw some demos` url have something like ‘?preset=leftsidebar’. It seems to be the same page with different options, I want to know how to do that?
Thank you!
And happy new year!!!