The Main world "Saga" is geared mainly for cooperative survival play.
This entire world is set to non-pvp, though you should still lock up your things to prevent stealing.
The "Saga-Pro" world is a PVP enabled world. This world also shares inventories with the "Saga" world, so you can begin play in one world and switch to the other at any time without having to start from scratch.
"Saga-Creative" is a purely creative world with seperate inventory from the other worlds. Players have access to infinate items and are encouraged to experiment with the ideas their minds think up.