The intent of this 30-page publication is to explain what happens when a function invokes itself and how it calculates the end result of a return statement, like for example,
return x * factorial(x-1)
When I call this function and ask for the 4 factorial, the function returns the value of 24. If you understand the steps that led to value 24 (how the calculation was made), then you don't need to read this booklet or do the exercises. However, if you are not sure how the above return statement comes up with 24 as a result since there are no obvious calculations in the script, then this booklet might help you grasp the concept.