Instructions are in each .mnu file - use Notepad to read the .mnu files.
Save .mnu files as a UTF-8 file if you want to use non-ASCII characters.

You can place .mnu and payload files the \_ISO\MAIMMENU folder or sub-folders - e.g. \_ISO\MAINMENU\MNU

For example, if the instructions say to place files in the \_ISO\xxxx\Utility folder:
If you place the .mnu file and .iso file in the \_ISO\MAINMENU\Utility folder, the entry will be listed in the Main Menu.
If you place the .mnu file and .iso file in the \_ISO\BACKUP\Utility folder, the menu entry will be listed in the BACKUP menu.
If you place the .mnu file and .iso file in the \_ISO\UTILITIES\Utility folder, it will be listed in the UTILITIES sub-Menu.
If you place the .mnu file and .iso file in the \_ISO\UTILITIES_MEMTEST\Utility folder, it will be listed in the UTILITIES - MEMTEST Sub-Sub-Menu.

Look at the instructions in the .mnu file for help. 
%MFOLDER% will always be set to the \_ISO\xxx folder.
$HOME$ will always be set to the same folder that the .mnu file is in.

See http://www.easy2boot.com/add-payload-files/list-of-tested-payload-files/ to see if a .mnu file is required for any particular payload.

