"You can download your registered programs and their manuals under "My Products" in the Service Center, your personal customer area. You will also find the serial numbers for your software here."
That user manual on the disc is likely identical to what is in the help menu of VEGAS by default. There's also the new features manual like VKmast mentioned, and tutorials available via VEGAS Hub as well. Youtube also contains a ton of useful tutorials, I find those far easier and more informative than a manual, as you can watch them do it. Then there's also the ability to make posts here with any questions you may have.
See this post to find links to download VEGAS Pro instruction manuals in PDF format. The information should be nearly identical to the help in the software."
The vcs.com website (Support > Downloads > Service Center) makes manuals available only for registered users of the program(s).