Here is a diagram for you to consult if you don't completely understand the directions.
Step 3: Assembly
First, cut out two one by one inch squares from the copy paper. Roll them both into cylinders and tape them. Tape one of the cylinder horizontally to the right hand lower side of the doorway about where you want the trip wire to go. Tape the other cylinder at the top right hand corner of the doorway vertically but angled slightly to the left (like the picture). Next, tape the scotch tape roll to the ceiling about three inches away from the wall (again look at the picture).