If necessary file or folder haven't added already to Hide List then do one of the following:
Drag-and-drop files or folders from "File and Folders Panel" to Hide List. Please, note that drag-and-dropping any folder will not automatically include all subfolders inside it. To add folders including subfolders select "Files"->"Add folders (with files)" menu option or click "Add items" toolbar button and select "Add folders (with files)".
Select File -> "Add items" menu option and choose one of the next items:
Add selected (default)
Add folders (with files)
Add mask
Select File -> "Add predefined" menu option and choose one of the next items:
My Documents
Cookies
Desktop content
Windows Favorites
Start menu
Click "Add items" button in Toolbar and select one of the next options:
Add selected (default)
Add folders (with files)
Add mask
Click "Add predefined" button in Toolbar and select one of the next options:
My Documents
Cookies
Desktop content
Windows Favorites
Start menu
Type in "Add quick mask" textbox at Toolbar if you would like to add a mask
Once any file/folder/mask is added to Hide List, it automatically becomes hidden.
Please, note that you cannot add files/folders that are critical to system (Windows folder, Hide My Folder etc.)

If necessary file or folder have already being added to Hide List but its status is set to "visible" then right-click it and select "Change status" to make it hidden.