Boiling is used for large joints of medium-quality meat, either fresh or salt, but boiling is really a misnomer, since the meat should actually be simmered very lazily and steadily throughout the cooking, and never boiled. The liquid is normally flavoured with vegetables, spices and herbs, but not seasoned with salt until halfway through the cooking, or not at all, in the case of salted meat, which may need soaking before the cooking starts.
There are two schools of thought about boiling: the meat can either be started in cold water and brought to the boil, or plunged straight into boiling water or stock. The first method is the more traditional one, but means that you must skim very carefully for the first half hour as masses of scum will rise. Then cover the pan and keep the heat fairly low so that the water simmers steadily. This method gives you a very good rich broth; by the second method, plunging into already boiling water or stock, most of the flavour remains trapped inside the meat. Either way the meat absorbs some of the flavour from the liquid and gives some of its own flavour in return.