OS is short for operating system, and in this context its related to the operating system your computer is running. I guess you're using windows?
Also, the version number I was referring to is the version number of Rockbox Utility. It's latest release is 1.2.3, the manual page talks about the version of the latest Rockbox release which is 3.4. I have no idea why it should be best to do a manual install. Our installer is Rockbox Utility, so if you are using it you aren't doing a manual install at all. The manual page holds the manual for Rockbox and is not related to a manual installation.
Your error description is unfortunately rather vague ("did not work" doesn't give me any hint what's going wrong). Please try to be more specific.