This is Quacktopia's first and main game. You can get your own plot when you log in by doing /p auto, this will bring you to your plot which you may build anything on [as long as it follows the rules].
You will get to your plot in future by doing /p h. You can let people build while you are online by doing /p add (player). You can let people always build by doing /p trust (player), then you can block a player coming into your plot by doing /p deny (player). You can clear the plot of everything by doing /p clear. The full list of commands can be found here.
The plots are 65 blocks by 65 blocks, you can build up to world height and down to bedrock. You only get ONE plot so make sure to make the space count! You cannot delete or move your plot.