From MediaMonkey Wiki
The Playlists view contains all Playlists and AutoPlaylists that are part of your collection. Playlists in this node can be organized hierarchically to suit your tastes. Note that Playlists and AutoPlaylists are stored within the MediaMonkey database--if you wish to use these playlists within another application, you must export them.
See: Exporting Playlists
Playlists are simply collections of Tracks arranged to play in a predefined order. When you add Tracks to the Library, a playlist is created by default, showing all of the songs that have been imported at that time. If you've added .m3u playlists into your collection, these will automatically appear in the 'Imported Playlists' folder.
See: Using Playlists
AutoPlaylists are collections of songs that are created dynamically based on a chosen set of criteria. As new Tracks are added to the Library or changed, AutoPlaylists adjust dynamically so that any new Tracks that match the chosen criteria are added, and others that no longer match the criteria are removed.
See: Using AutoPlaylists