The idea is to move around in 3d until you find an empty space where you want your guestbook entry to be. You move around by using your scroll bars (up and down/side to side) and two keyboard keys. Your F key will move you forward your B key will move you back.
When you decide on a spot, click the yellow CLICK HERE TO BARF AT CURRENT LOCATION button.
A form will appear and you can type whatever message you wish. then press submit button.

That's all there is to it!
Have fun!!