To switch from the standard Duplicate mode (where what you see on the laptop is replicated on the projector/screen) to Extended mode (where you can have different things on the laptop and different things on the projector/screen) it should just be a case of doing the following:
Press Windows Key + P together
A new menu should then show down 1 side
Then click on the 'Extend' option
You should now see a 'blank' screen on the projector/screen to what's showing on the laptop
Now it should be possible to drag windows (by clicking in the title bar at the top and holding button down) across from the laptop to the projector/screen for the class to view, whilst other windows, like emails, just remain visible on the laptop only
You can also do something similar with Powerpoint slideshows by going to 'Slide Show' along the top in Powerpoint then amending the 'Monitor' drop down to specify which screen (laptop or projector/screen) the Powerpoint slideshow should be displayed on - this setting might take some getting use to though
