The purpose of the Monitor Watch Folder task is to monitor the chosen folder for subfolders being added and process the audio files within the new folders. It will ignore any existing files and folders that existed in the folder before starting the task, of course these could be processed with the Fix Songs task in the normal way.
So you will only see Monitor Watch Folder do anything if you add a folder containing music files or containing subfolders with music files directly to the chosen folder. These will then be processed and Monitor Watch Folder will continue to do run until you cancel it, at this point it will generate a report and then stop.
It is also worth noting the task will ignore individual music files added directly to the selected folder, this is because SongKong is primarily an album based folder and if individual files are added at the top level it is difficult to determine when the complete album has been added.