Hi, Jeffrey! You don't technically have to "link" your Advance Dining Reservations and your Disney Dining Plan together before you go. When dining, your server will ask you if you are on one of the Disney Dining Plans. Presenting your Key to the World card is all it takes to use the plan.
You can, however, get all of this information gathered in one place before you go. From the
Walt Disney World home page, log in, and then select the My Disney Vacation link. That will bring you to the Planning Center page. From there, select My Reservations. Using your confirmation numbers, both vacation and dining, you can get the Advance Dining Reservations and your vacation package linked together. If all else fails, you can visit Guest Services upon arrival, and they will help you. I just like to have things in order before arrival. Happy planning and have a Magical vacation!