This guide refers to outdated and obsolete concepts from CLtL1. I'd recommend reading http://www.gigamonkeys.com/book/programming-in-the-large-pac... from Practical Common Lisp or just the relevant portions of the spec at http://l1sp.org/cl/11.1.1 - it's pretty readable. One non-recommended approach: guess and be disappointed when your intuition doesn't match how it actually works.