Our story so far is intelligible, though perhaps not very dramatic. Let's add some excitement by making some common mistakes. There's an important moral for this last piece of the story. Using subscripts outside the valid range for your array is a very common, and often very tricky, program error. Pictures of information holders.
Programmers often draw pictures to help keep track of what values are in what information holders.
Such a picture just has a little box for each information holder, with arrays being drawn as columns of boxes next to each other. The values are written into the boxes, and erased and replaced as needed when the values change. You will find it useful to use this kind of picture while you work on the exercise. Even very experienced people do this, because otherwise its just too easy to forget what is where. Anytime you need to do something with an array you want to think first of this idea.