Hi Tony, the PiDrive 1TB is the Berryboot Edition with WD Berryboot installer preloaded on the microSD card. The menu allows selection of the destination device for installation of downloaded OSes. The selection box should show the SDcard and also the PiDrive (PiDrive starts with "sda...."). Are you seeing the "sda..." option in the destination selector?
The Foundation Edition PiDrives and software use a different software installer (based on the Raspberry Pi Foundation's "NOOBS" software). Our Foundation Edition software installs Raspbian PIXEL and multiple instances of Raspbian Lite so multiple command-line programming projects can be supported on the same setup. You can install either WD Berryboot or Foundation Edition software on all PiDrives. Software download and supporting documentation for our PiDrive software is at the link below.
Let me know if you're seeing the "sda...." destination option. If not, it would help a lot if you could send a photo of your set-up, including the 5V power adapter and USB power cable. If you'd like to provide this, please send it to my email: email@example.com.