You should be able to open the manual by pushing F1 or via the 1st item in the help menu, unless the menu or toolbar it's on has been edited to remove it.
If the help viewer is opening but not displaying the manual correctly, it's likely your Windows Help components need repairing. See our Help file does not display correctly guide for what to do if you're seeing that problem.
(Java is not required for any part of Opus, by the way. Javascript, despite its similar name, is totally separate from Java and built into Windows so you shouldn't have to worry about it, either.)
You can also access an online version of the manual via the web. (The F1 version is usually preferable, though, since it's quicker.)
If you tag the files and then use grouping, you'll get something like this:
If you want to see all the files with a particular tag, using Tools > Find Panel > Advanced lets you do that:
