The Network Expect manual page contains a lot of detail about Network Expect and its syntax.
There is also a page with Frequently Asked Questions.
And of course, no documentation is good without a bunch of examples.
While NetworkExpect is usually used via scripts, it can also be used interactively by issuing commands from a prompt. A sample InteractiveSession session with NetworkExpect shows some of the most important features of NetworkExpect.
Introduction to Network Expect - presented in a Forum for Incident Response and Security Teams (FIRST) Technical Colloquium (TC) in Washington, DC on March 1, 2007.