Marinading is not a cooking method actually, but a way of preparing foods, usually meat or fish, for subsequent cooking. A marinade is an appropriately seasoned liquid, that may be cooked or uncooked, in which meat or fish is left for sometime. The idea is to impart to the food so treated all the flavors of the marinade. The process also softens the fibers, and if it is game you marinade, the addition of some papain will speed up this process.
The time foods should be marinated depends very much on size and texture. Large cuts of meat or venison may be marinaded for several days in the winter, but not much more than 24 hours in the summer. Smaller cuts require shorter periods. Marinading can make an indifferent cut of meat positively delicious, but it has two disadvantages. First, it requires forethought and premeditation like the perfect murder. Second, it takes time. You cannot very well start it an hour before meal time.