The purpose of brining is to tenderize the meat while adding flavor. A solution of salt is dissolved in water and meat is then submerged for a set amount of time, changing the cell structure and making it more moist and, often, more flavorful. The basic formula for a brine is 1/2 cup to 1 1/2 cups kosher salt for every gallon of liquid (whether water, juice, stock or beer). You can also add sugar and any other seasonings to taste; try herbs, garlic or peppercorns. Brining saturates the meat with the flavor of these seasonings. Unlike marinating, which flavors the outside, brining gives you deeper flavor and increased moisture.
The larger the meat, the longer it should brine; while shrimp only need about half an hour, a whole turkey takes 6 to 8 hours or so. Add ice to the brine to keep it under 40 degrees Fahrenheit in case you don't have room in the refrigerator.
Once you're done brining, remove the meat from the brine, pat it dry and cook it the same way you would otherwise.