Summarize the following:
On the morning of the day you want to roast the turkey or the night before, remove the brine from the refrigerator. Pour it into a 5 US gal (19 l) food-safe bucket or cooler. Mix in the ice water. Consider using a 5 US gal (19 l) drink cooler. These have good insulation and a drain spout for easy clean up. Take the turkey from the refrigerator and remove the innards. Discard the innards and the pop-up thermometer if your turkey has one. Put the turkey breast-side down in the brine-filled container. The turkey should be completely covered in brine. If it isn't, place a heavy plate or dish on the turkey to weigh it down. Cover the bucket and refrigerate the turkey while it brines. If you're using a cooler with a lid, screw the lid on and leave it in a cool place while the turkey brines. The cooler with the turkey and brine should keep the turkey at 38 °F (3 °C) or below. If you think the cooler isn't keeping the turkey cold enough, refrigerate it.

Summary:
Mix the brine with 1 gallon (3.8 l) ice water in a large container. Submerge the thawed turkey in the brine. Chill the turkey in the brine for 8 to 16 hours.