How to do Pattern Matching in Common Lisp
I think you may want the CL-Unification library: http://common-lisp.net/project/cl-unification/
I don't want to short circuit any learning you need to do for school (if that is the context in which this project is necessitated), but you could study the cl-ppcre library, http://weitz.de/cl-ppcre/, to see how an experienced Lisper does it. You could download the source and study it to understand. I would also second the book by Norvig, http://norvig.com/paip.html, mentioned above. You can learn so much from that book.
Simple pattern matching functionality is explained in various Lisp books.
Lisp, 3rd edition, Winston/Horn
Paradigms of Artificial Intelligence Programming, Case Studies in Common Lisp, Peter Norvig
and others.
Above books explain implementing pattern matching in Lisp very well.
Libraries exist, for example trivia, cl-match, and various others.