Under the File menu click on "Add to Library..." and select the root folder of the files that you want to add. This will add everything in that folder and all subfolders, organize them, set volume limits, and download album info.
Under the File menu click on "Add to Library..." and select the root folder of the files that you want to add. This will add everything in that folder and all subfolders, organize them, set volume limits, and download album info.