ROBLOX is an online game that allows you to create virtual 3D worlds out of lego-like pieces.
It's easy to get started. Simply register online at the official website where you will be able to create your own character. These characters can be customised from head to toe and used to help you build your environment. The game is free, but you may also upgrade to a paid version available with additional functionality. Since it's an online community game, you can also access worlds created by other players and interact with them.