Once booted, the unRAID server configuration is accessable from your web browser. Point your browser at the IP address of the unRAID machine and you'll be greeted by the configuration page.
Figure 2: Main Configuration Page
From here, you can add your disks from the drop-downs under "Devices". In the basic server package, you're only allowed three disks, one of which must be used for parity information.
Figure 3: Device Configuration Page
Returning to the main screen will show your newly added disks. Format the drives by simply clicking the "Format" button in the Command Area.
Figure 4: Formatting the Drives
Figure 5: Formatting in Process
unRAID will happily run without a parity drive, leaving you the option to add one later. However, as with all RAID arrays that use parity, it takes time to build the parity drive once installed in an array. This was a little over 90 minutes for a 300 GB parity drive for me.