Both CD and DVD duplication work in the same manner.
The blank disc are placed into the duplication system, then the discs are burned with whatever was on your master and the output can then either be printed or packaged. With the Duplication process, your allowed the ability to control the exact number of discs that you wish to produce. This is great advantage if you only wish to product smaller quantities of discs.
With the advances in the printers and disc coatings, duplication can have a huge advantage over replication because the printing of the disc can be much more detailed and actually be full photographic quality.