The Screen is a versatile block that can display all kinds of information. This depends on the modules you have installed. The Screen needs power that is remotely supplied by a nearby Screen Controller
Right click with an empty hand to open the Screen user interface
In the GUI you can install modules (or you can install them by right clicking the module on the screen)
Many modules (like the energy module) need a target to work on. To set that target you must first sneak right click the module on the machine you want to monitor
When the module is installed in the Screen there are also various display options that you can set by opening the specific module GUI (accessed through the normal Screen GUI)
In that GUI you can also enable 'full bright' mode and by using the wrench you can change the size and transparency of the screen