Recursion HALP

Hey /prog/, I must say my understanding of recursion is shit (never really dealt with recursion in all my days of writing bad code). How should I go about thinking about it?

inb4 flaming: I understand the recursive concept in some contexts, such as when it is used in a factorial function, but when it starts getting more ambiguous (say, exercise 5, ch. 2 from ANSI Common Lisp) it's ugly.

inb4 RECURSE MY ANUS

>>13
Are you this fucking stupid? Maybe you should stop giving shit advice and actually read a book. With that you fucking stupid shit, you are still being ambigous.

First off you don't specify the evaluation order. At what point and time do you actually calculate the values in the recursion? Second thing you fucking moron, you don't give a clear definition of the term "variable". Is the variable meant in the C/C++ sense or in the math sense? Finally, not every computer uses a stack.