This book isn't a language definition for Scheme, or a manual for using
any particular Scheme implementation. There is a free language definition
document for Scheme, easily available via the internet, called the Revised
Scheme Report. (There's also an IEEE standard.) We recommend getting the
Scheme report and printing it out, or browsing the html version with
a web browser.
(http://www.cs.indiana.edu/scheme-repository/doc.standards.html
It's not very big, because Scheme is a pretty small language. We also
recommend having a look at the documentation for the particular implementation
of Scheme you're using.
On the other hand, this book may serve as a passable approximation of a language manual most of the time. It describes all of the important features of standard Scheme, clearly enough that you can use them for most purposes. A near-complete description is possible because Scheme is very clean and "orthogonal"---most of its features don't interact in surprising ways, so if you understand Scheme, and do the "Scheme-ish" thing, Scheme will generally do what you expect.
For more information on Scheme, particular Scheme implementations, and
so on, see the FAQ (Frequently Asked Questions) list on the usenet newsgroup
comp.lang.scheme. It's available from the Scheme Repository
via anonymous internet ftp from ftp.cs.indiana.edu in the
directory pub/scheme-repository. Or if you're a World Wide Web
user, visit the Scheme repository at
http://www.cs.indiana.edu/scheme-repository. The Scheme
repository contains several free implementations of Scheme, as well as a
variety of useful programs, libraries, and papers.