RFTools Screen
A screen by default displays nothing. In order to let it display useful things you need to insert modules in the GUI. Most modules can be configured in some way. When a configured module is removed from a screen it will keep its configuration. So it is easy to move configured modules between screens.
The power that a screen consumes depends on the modules that are in it. A screen will only display something if it is actually connected to a controller and if the controller has enough power for the screen to run.
You can hit a screen with a wrench to change the size (from 1x1 to 2x2) and to toggle it to transparent mode.
You can also select the screen with a dye to change the color.
Here are a few example screens:
