Opening Plugin File Systems
You can easily open (connect to) plugin file system in the Change Drive Menu and in the Drive Bar. If you don't find some file system in this menu/bar, find appropriate plugin in the Plugins Manager dialog box and set the Show FS item in Change Drive menu and Drive bar check box. Also see Changing Directory for other ways of opening (changing directory to) plugin file system, mainly: Commands/Change Directory (Shift+F7) and Edit/Paste (Ctrl+V).
When you open file system in panel, you can work with files and directories in it. Just focus or select them and use View, Copy and Move (it works in both directions - from/to other panel), Delete, Copy to and Paste from clipboard, Compare Directories, and other commands (search menu for enabled commands). You can also use commands from context menu (use right mouse click or Shift+F10).
The View command copies focused file from plugin file system to temporary directory. This file is then opened in Viewer. Plugin can use cache for such files so if you try to view the file second time, it's just displayed from temporary directory (to get the recent version of file, use Refresh).