(Denna sida finns bara på engelska.)
The computer rooms have one projector each. Turn them on with the button PC1 at the wall. If connecting to one of the GNU/Linux computers in the room, note that their monitors are connected to DVI on the computer, so let them be and connect the projector as well so both are connected at the same time.
Choose System→Preferences→Display to adjust how the two displays should be used. Most of the time you will probably want to Mirror screens to show the same contents on both.
If you are using sound, connect the purple connector to the blue socket on the computer.
If you don’t want to show the same thing on both displays but instead put the side by side, maybe to show something in fullscreen to the whole room while you are looking at something else, sometimes you don’t get the panels where you want them. In that case hold down Alt while grabbing a panel with the mouse, and you can drag it to the right place.