For debugging purpose only. If there is no session going on or if you are not connected to the net, you can simply test gp by activating two gp on your computer. After 30 seconds. you will see two windows for each gp. Using the palette, fill a rectangle of the local image with a color. It will appear on both global images at the allocated place.
Placement is done by software.
If the palette is only black and write, try to kill your browser or the other application which could take all colors available. Places become definitive after 5 minutes. This action opens the message window. Click in the corresponding global image on a participant place and look at the 'Send message to'. Write a small text in the 'Send message to' window followed by 'return'.