I know that chumming was originally used for saltwater fishing. Can you tell me how to do it and under what circumstances it’s the most effective?

Also known as ground-bait, chum is considered essential when fishing for saltwater fish.  Most saltwater fishermen believe that setting up your ground-bait or chum is without a question, the first thing you do when you get to your fishing spot.  The goal of using ground-bait or chum is to draw the fish from the area as close to your bait as you can get them.  Chumming incorrectly, can actually draw the fish away from you, pretty much ending any hopes you may have had of a good catch.  While there are many commercial chums available, they can be rather expensive and most fishermen choose to make their own.  While there are several methods that you can actually use when chumming, I believe actually using a chumbag works the best in shallow water.  The concept is fairly simple and you can either buy a bag or make your own.  Fill the bag with the chum of your choice (will depend on where you’re fishing and what you’re trying to catch), and hang it from the stern of your boat.  You will quickly have a chum slick, that can be as long as several hundred yards.  The first fish that you should see attacking the chum will be the baitfish.  These will in turn, draw the gamefish.