This manual page is not meant to be exhaustive. The complete documentation for this version of TeX can be found in the info file or manual Web2C: A TeX implementation.
The AmSTeX language is described in the book The Joy of TeX. AmSTeX is a TeX macro package, not a modification to the TeX source program, so all the capabilities described in tex(1) are present.
The AmSTeX macros encourage writers to think about the content of their documents, rather than the form. The ideal, not always realized, is to have no formatting commands (like “switch to italic” or “skip 2 picas”) in the document at all; instead, everything is done by specific markup instructions: “emphasize”, “start a section”.
For authors more familiar with LaTeX, an AMS-supported package called amsmath.sty is available, among others.
Documentation for AmSTeX, typesettable by TeX.
Documentation for AMS fonts, typesettable by TeX.
latex(1), tex(1), slitex(1).
Michael Spivak, The Joy of TeX, 2nd edition, American Mathematical Society, 1990, ISBN 0-8218-2997-1.