Step 2: Assemble the Frame
Flip your mat board frame (or equivalent) over so you're looking at the "back." If you are using a stiff piece of plastic as your screen, position one edge so that it is close to one wide edge of the frame (as in the picture); this will be the "bottom" of the frame, and the battery pack needs something solid to attach to. If you are using velum, position it higher so that as much of the bottom edge of the frame is exposed (when using velum, you will want to attach the battery pack directly to the mat board).
Next, tape the left and right edges of the screen to the back of the frame. Make sure the tape does not overlap with the window, or it will show through when the screen is illuminated from behind.