Look on your wrapper on the bird and see if it says that it has been brined or if it is Kosher. If so the you would just do well to cook the bird. Here is the thing about a brine though, it is osmotic. So the inside of the bird and the outside will equalize with salt over the period of X hours.
I like to do on the stovetop, 3 gallons of water. 2 cups Kosher Salt. 3 Frozen Applejuice concentrates and a 1/2 cup sugar. Heat this and any other seasonings (like garlic, black peppercorns, chilis) until boiling and then put into a cooler or bucket or other brineing vessle along with a bag of ice. Then submerge your turkey overnight and keep in the fridge (if in a cooler, disregard this. If in a bucket then put in fridge or cooler with ice).
Then take the bird out the morning of the BBQ and place into a pan. With 3 x gallon ziplocs of ice, place one inside the cavity and one on each breast, leaving the legs open to the air. This chills the breast to about 35*f and lets the legs get to 65*f while the BBQ is heating up. Then breast side up into the center of the BBQ, pan underneath with two light homebrews (or light lager, nothing hoppy) and 4 cups of water and an onion and garlic head halved, indirect heat for about 4-5 hours at 300-325. Breasts at 165 and legs at 175 are a perfect bird in the end. Rest for 30 minutes and enjoy!
Good luck, this turned out a great turkey on T-Day this year.
EDIT: If you want a good rub:
1/4 cup Black Pepper
1/4 cup Granulated Garlic
1/4 cup Onion Powder
1 tblsp Smoked Paprika
1tblsp Mustard Powder
1 tblsp Cayenne (more if you like)
1 tblsp Kosher Salt (optional here with the brine)
Rub this all over the bird after you pat it dry from the brineing. It makes the skin super delicious. Rub under the skin if you want a nice crust on the breasts.