When a single file is too large to fit onto a single DVD, that file is spanned across more than one DVD. Movies or files containing your email information, such as .PST files for MS Outlook, can often be very large.
The extra DVDs are called supplement disks and arrive with labels like this: Supplement Disk A to Vol. X. The number represented by A is the unique ID for each supplement disk. The number represented by X is the unique ID for the specific restore volume that the supplement belongs to.
To restore a spanned file, you must copy the contents of all the DVDs for that file into the same folder. This includes the restore volume DVD for the spanned file, followed by each of its supplement disks. Then you must decrypt the shipping encryption, uncompressing and reconstructing the file into that folder. Finally, you can move the file into its final location.
If you chose personal encryption, you might prefer to start by unlocking the shipping encryption and putting the resulting files into a temporary folder, perhaps on your desktop. From that location, you can decrypt using your personal key and in that process put your files into their final destination on your computer.