To import previously downloaded songs into the iTunes Library.
From the File menu select whether to import a single song, or a group of songs:
Select Add File to Library to import a single song, or
Select Add Folder to Library to import all songs in a folder (and sub-folders)
In the dialog box that opens, navigate to NETWORK-DATA/Music/New which is our standard location for downloading new music.
Select the appropriate song or folder.
For Example: To import all the downloaded music from AllTunes, select the AllTunes folder within the New folder.
Click Select Folder for folders, or Open for single file, and wait for iTunes to add all the songs to the Library catalog.
Document the information about the imported songs.
Once you have finished documenting an album in iTunes, go back to Windows Explorer and move that album from the New folder to the To Be Deleted folder. This will help prevent the same album being imported multiple times and creating multiple copies of the songs in iTunes.