Salt cod is a dried and salted version of the fresh cod fish. Because it can be stored for long periods and transported easily, salt cod was historically a very important source of protein in many different cultures. To use soak in water for 24 hours, changing the water 3-4 times. After this it can be used much like fresh fish.
Alternatively you can boil it in water for 15 - 30 minutes, then soak in fresh water for 30 minutes. The fish will still retain some of the salty flavor and is excellent for making stews, stir fried with okras, making Bul Jol or sauteeing with herbs.