Before discussing the phenomena of single and multiple slit diffraction there are a few operating instructions to note with regard to the use of the laser.
The laser beam is very intense. Don't look directly into the laser when it is operating. The spot may be viewed only after it is diffusely reflected from a surface. There is usually enough dust or other imperfections on lenses or mirrors to show the location of the beam. Always use a piece of paper or other non-shiny surface to observe the laser light. Your finger is often the best visual detector.
The laser is easy to operate, simply plug it in and turn on the switch at the end of the case. Normal precautions applicable to precision equipment should be observed; that is, don't bang things around, don't position the laser where it might fall or be easily bumped.
Four important aspects of laser light are: (1) it is very bright, (2) it is monochromatic, (3) the beam has a very small angular divergence, and (4) it is spatially coherent. The last feature is the one that produces the most interesting effects. For example, note the granular appearance of the beam spot on the wall or paper screen. This is due to diffraction effects of the aperture of your eye. Note that they appear to change size when you move your eye closer to or further from the beam spot. The spot may be enlarged for this purpose with one of the lenses supplied.