Artemia (brine shrimp) usually come in one of two ways: frozen or as eggs.

If you buy frozen brine shrimp, all you need to you is to de-freeze them and feed them to your fish. All fish love brine shrimp. Note that not all frozen brine shrimp have the same size. Larger ones can be hard for smaller fish to eat. If they cannot eat them, the left-over shrimp will end up rotting in your tank. Also, not all fish do well on a protein-rich diet. Many Malawi cichlids, for instance, need mainly plant or algae based food. We always de-freeze the artemia, but other people just throw the frozen cube in the tank. Apparently this is alright, but to us it seems cold for the fish to have in its mouth and intestines. Better avoid.

If you buy brine shrimp eggs, you have to hatch the shrimp yourself. You cannot feed unhatched eggs to your fish - they will only the water, but not be eaten.
Hatching artemia eggs is not necessarily very difficult, but there are some factors to keep into account: you will need a high PH, copious aeration, sufficient light, temperature between 22-28 degrees celcius, and about two tablespoons of salt per liter water. There are kits available to hatch brine shrimp eggs. If you want to breed fish, a constant supply of freshly hatch brine shrimp will be very helpful, and we do recommend buying one or two brine shrimp hatching kits to get an optimal hatching rate and keep your supply going.