The examples for this book use Pure Data (Pd), and to understand them you will have to learn at least something about Pd itself. Pd is an environment for quickly realizing computer music applications, primarily intended for live music performances. Pd can be used for other media as well, but we won't go into that here.
Several other patchable audio DSP environments exist besides Pd. The most widely used one is certainly Barry Vercoe's Csound [Bou00], which differs from Pd in being text-based (not GUI-based). This is an advantage in some respects and a disadvantage in others. Csound is better adapted than Pd for batch processing and it handles polyphony much better than Pd does. On the other hand, Pd has a better developed real-time control structure than Csound. Genealogically, Csound belongs to the so-called Music N languages [Mat69, pp.115-172].
Another open-source alternative in wide use is James McCartney's SuperCollider, which is also more text oriented than Pd, but like Pd is explicitly designed for real-time use. SuperCollider has powerful linguistic constructs which make it a more suitable tool than Csound for tasks like writing loops or maintaining complex data structures.
Finally, Pd has a widely-used sibling, Cycling74's commercial program Max/MSP (the others named here are all open source). Both beginners and system managers running multi-user, multi-purpose computer labs will find Max/MSP better supported and documented than Pd. It's possible to take knowledge of Pd and apply it in Max/MSP and vice versa, and even to port patches from one to the other, but the two aren't truly compatible.