Check your C:\netos74\Documentation directory
You'll see a "Programmer_Guide.pdf". Read Part 4 in that guide. That's the easiest way to do it. Also, check out some of the example programs in the development environment, under "File->New->NET+OS Sample Project". It'll generate the C code, but also includes some sample HTML pages they used in the HTML-to-C Compiler you'll read about in the "Programmer_Guide.pdf"
For more advanced pages, read the "Advanced_Web_Server_Toolkit.pdf". The AWS uses pages that are compiled with a utility called PBuilder. PBuilder is accessed via the command prompt in Windows (Start->type in "cmd" to the search box).
PBuilder and the AWS are briefly described in Part 5 of the "Programmer_Guide.pdf", as well. See page 154, specifically.