What is the purpose of the PS3 game "Little Big Planet"?

I looked at some gameplay videos but am still unsure about what it is about...is it a puzzle game like Lemmings way back in the day? Do you create ways for the little sack characters to reach a goal? I'm not really sure what the heck you do in it but it looks like it could be a fun puzzle game...do you know what you do in the game?