Symbolic computation is considered by some to be one of the most complicated math subjects to understand. Symbolic computation relates to using machines such as computers to perform mathematic equations. The concept can be a bit vague and hard to grasp, so many different types of software have been developed and many tutorials are available to help people understand how symbolic computation works.
Common Lisp: Full text of Common Lisp: A Gentle Introduction to Symbolic Computation written by David S. Touretzky of Carnegie Mellon University. It comes with free software too!
SACNet: Homepage of the Symbolic Mathematical Computation Information Center, it provides a lot of information on symbolic computation.