You create a backup stage to your NAS and then add a duplicate stage to your tape.
You will only see media sets when you have defined tape and/or disk cartridge storage. Otherwise, you would not see media sets. Disk Storage which is defined for fixed disk is managed by DLM.
Click on the server that you want to backup and click on the Backup button in the ribbon bar and you would be present with the option to backup to which type of storage.
After you have selected the type of storage, you would see a window with 2 sub-pane. Click Edit on the left-hand pane and you would see the selection list. The right sub-pane will allow you to add another stage, e.g. duplicate.
If you don't have a tape drive all of the options relating to tape drives (including duplicate from disk to tape) will be hidden from the console - as why show you something you can't actually do. BE 2012 is designed to hide things you can't do to reduced confusion (so in a similar way you won't see Exchange options if the server you are trying to backup does not have Exchnage installed on it)
If you want top test this sort of thing in a lab you must use a tape device (which does of course also mean it can't be a virtualized media server.)
