Thomas Shaffner released Microsoft GW-BASIC User's Guide and User's Reference to the web and you can already find copies of it easily (try here, here, here or this PDF version which fits nicely on the Kindle screen). Download a ZIP archive of GWMAN on the archived KindlyRat GWBASIC page or on my downloads.

For more command information, be sure to search the blog. As I learn things and want to teach them, you'll find them categorized under tutorials and techniques.