You could start by formulating the task for the students. After that, ask them to start and, if necessary, guide them if questions arise.

In practice, it might be a good idea to do this with the students. For this, it would be good to use a flashlight equipped with a magnet and paper clips. In this way, it is possible to draw rays on the board in such a way that the students can see it, and it is necessary to do significantly less individual guidance.

When the result is on the board, students can be asked how many light rays are emitted from a small light source.

As a comment on the possible answers, it can be explained that we selected three rays of light with the help of slotted paper and transferred them to the drawing. If we had placed the slit system a little differently, we would have obtained an image with slightly shifted rays. If we were to draw the rays produced at all the possible locations of the slits, we would end up with one densely packed area of ​​rays, which is the same patch of light we started the exercise with.