Giblets is the term used to described the heart, liver, and gizzard of poultry, and often the neck, too. In processed birds, these parts are put in a bag placed in the cavity of the bird and must be removed before cooking. They are great for making a quick stock or to enrich gravies and stuffings, so don't throw them out.
You can buy chicken livers separately from whole chickens. You can use wing tips to add flavor to a quick chicken broth if there is no neck.
You get what you get inside the bird you bought. Sometimes this means more (or less) of each gilbet.
To make a stock, cover the neck, gizzard, and heart with cold water and add some chopped carrot, onion, and parsley stems. Simmer for 45 minutes or so and strain. If you're making giblet gravy, dice the heart and gizzard and pull the meat from the neck bone and add them to the gravy toward the end of heating. If you would like to add the liver, saute it separately, chop it and add it to the gravy along with the other giblets. Sauteed giblets are also good diced and added to stuffing.
The giblets will keep for a few days in the refrigerator, longer if frozen.