The bellow image is what we are aiming for

STEP ONE


Using the RECTANGLE tool, draw a a medium sized square on your art board.
If you're unsure of which tool to use, the image above will guide you. The rectangle tool is highlighted in red

STEP TWO
Using the white cursor tool on your tool bar click on the square.

STEP THREE
Using your cursor click on the bottom right point of the square. You need to make sure that the points turn WHITE.

See in the above image how all the points except for the one that you have clicked on are white? This is what we need to create the beam.

STEP FOUR
Now you need to hold that point down (the one that is circled) and then drag the point on an angle. You should end up with the image below: