brine

Salt food ahead of cooking so the seasoning reaches well past the surface and the meat holds on to more of its juices instead of squeezing them out. It comes in two forms that are not interchangeable: a wet brine dissolves the salt in water and submerges the food, while a dry brine rubs the salt on directly and adds no water at all. They want different amounts of salt, different timings, and different equipment.

How to do it

Which form you want depends mostly on refrigerator space and on what you want from the surface. A wet brine is the more forgiving of the two and the better choice for very lean cuts that dry out easily. A dry brine needs no container big enough to submerge a turkey, and because it drives surface moisture off rather than adding more, it gives noticeably better browning and crisper skin. Either way the food ends up seasoned all the way through rather than only on the outside, and either way the surface has to be dry before it meets heat. Salt quantity and time both matter, and more of either is not better -- an over-brined piece goes past seasoned into salty, with a springy, faintly cured texture that does not cook out.

Wet brine: salt dissolved in water

Pick a non-reactive container -- glass, food-grade plastic, stainless steel, or a brining bag -- big enough to hold the food fully submerged and still fit in the refrigerator. A strongly acidic brine can react with aluminum or bare cast iron.
Dissolve the salt completely in the water before the food goes anywhere near it, along with any sugar and aromatics. Undissolved salt sitting on the bottom is salt that is not seasoning anything.
If any of the water was heated to help the salt dissolve, cool the solution completely first -- fastest by stirring the hot portion into the remaining cold water or ice. Warm liquid plus raw meat is both a food-safety problem and a way to start cooking the exterior before cooking begins.
Submerge the food, weighting it down if it floats, and keep it refrigerated for the whole soak. Scale the time to the cut: a thin chop or a few chicken breasts want under an hour, a thick roast a few hours, a whole bird most of a day.
Lift the food out, discard the brine, and pat the surface very dry with paper towels. Leftover surface water is the single biggest reason brined meat browns poorly.
Season whatever comes next cautiously. The food is already salted through, so the usual amount of salt on top will be too much.

Dry brine: salt rubbed on directly

Pat the food dry, then rub salt evenly over every surface, including inside the cavity of a bird. About 1/2 to 3/4 tsp of kosher salt per 500 g / 1 lb is a reasonable starting point -- see kosher salt, since the same spoonful of table salt is considerably saltier.
Set the food on a rack over a tray and refrigerate it uncovered. Uncovered is deliberate: circulating cold air dries the surface, and a dry surface is what browns and crisps.
Give it time. A few hours seasons the surface; overnight, and up to about 24 hours for a large cut, lets the salt draw moisture out, dissolve into it, and be reabsorbed carrying the seasoning inward. The one window to avoid is short: roughly the half hour just after salting, when the salt has pulled water to the surface but has not been drawn back in yet -- that is the worst of both states.
Do not rinse it off. Unlike a wet brine, the salt is the seasoning and it has already gone in; rinsing washes away the dry surface the whole wait was spent building.
Cook it straight from the refrigerator, or let it sit out briefly first, and season whatever follows cautiously, as with a wet brine.

Common pitfalls

Brining too long -- the meat can turn excessively salty or take on a springy, cured texture.
Using warm brine -- it raises food-safety concerns and can start cooking the exterior of the food before it even reaches the pot.
Skipping the pat-dry step -- wet skin or a wet chop steams instead of browning once it hits the heat.
Brining in a reactive container -- a strongly acidic brine can react with some metals.
Brining meat that's already salted -- some poultry is sold pre-injected with a salt solution ('enhanced' or 'seasoned'); brining it again can make it far too salty.

Why it works

Salt loosens the structure of muscle proteins, making them better able to hold onto water as the meat cooks, and it diffuses inward over time, seasoning the meat more deeply than surface seasoning alone can reach. A wet brine can also add to the total water already present in the meat, so even though cooking inevitably drives some moisture back out, properly brined meat often finishes juicier than untreated meat cooked the same way. Dry brining runs a different sequence: salt first pulls moisture to the surface, that liquid dissolves the salt sitting there, and the resulting concentrated brine is then gradually reabsorbed. Despite the common shorthand, this isn't simple osmosis -- protein chemistry and diffusion are doing the real work.

Equipment

Use a nonreactive, food-safe container -- stainless steel, glass, or food-safe plastic. A large zipper bag is convenient because it needs less brine to fully surround the food. For a whole bird, make sure both the container and the bird will actually fit in the refrigerator for the duration. A digital scale is worth using for the salt itself: a tablespoon of one salt can weigh considerably more than a tablespoon of another, so weighing it is more reliable than measuring by volume.