Help > About Directory Opus in the default toolbars.
Push F1 from within the program a local copy of the manual for the version you have installed will open.
You can also find web and PDF versions of the manual by clicking Manual in the links bar of the main Opus site, or the direct link to the web version at the top of each page on this forum where it says Opus Manual.
The web version is usually the latest stable release, so if you are using beta releases your local copy may have newer information.
It depends why the files are being hidden. Are they system files as well (both H and S attributes set)? If so then the system files option also needs to be set.
If they still don't show up, what happens if you use the Folder > Clear Local Name Filters menu item? (If you're having trouble locating it, it's shown just below the green rectangle in the first screenshot here.)