In this tutorial I will show you how to add a cool beam of light coming from the computer of this picture. First off, save the following picture so that you can use it while you do the tut, or use one of your own

make new layer, set the mode to"color" And fill it with a color of your choice. I chose purple/blue

Now merge all your layers so that you only have 1 left.

Now select the side of the beam that will be coming out of the computer, as shown below

 

Take out your dodge tool.

Now using the mouse, brighten your selection

Brighten it again, but this time, just next to the monitor of the computer

Now make a new selection above to the computer to act as the other part of the beam

Do the same thing with this selection as the one above

Now brighten the image where the light will be hitting the area around it.

The darken the parts were the light will not be hitting it.

Now just take out your blur and smudge tool and play around with it until you are satisfied.

And now your done, this is just a basic method you can use to make a lot of cool effects. I hope you have fun with it!