The Library (in the upper-left part of the RecordForAll window) is where RecordForAll keeps a list of all the files you've imported. Sound effects, your takes, any background ambient noise sounds, and, of course, your music—the Library serves as the source of material for your Playlist.
Use the Library to see all the tracks you've added to RecordForAll. You
can also play a preview of any file in the Library and review such details
as the artist, title, and length.

See also