You can use that voucher to access the passholder portion of Disney's website and book your room with BRP!
Just type in the #'s...if you need help, there are already threads about that ..or just ask here! Most of the confusion is with the last box on the site. My voucher has " mm/dd/yyyy WDW 123 TR: 45 67" at the end. I put 67 in that last box and it works for me.