How to use amsmath package in LaTeX

[Charles Blair <c-blair@uiuc.edu>]

   I have installed tetex-base and other packages, but a simple
test file beginning

\documentclass[12pt]{article}
\usepackage{amsmath}

gives an error message (I have been able to process TeX and LaTeX
files that do not use amsmath).

   Is this package contained in tetex-extras, or does something
else have to be done to install it?