You put whatever you like (e.g. cold cuts, fruit, potatoes, mushrooms) into individual little pans and top them with raclette cheese (or other varieties). Then you put it into the raclette grill, which is a broiler with a strong top heating element, that will melt the cheese over the content of your pan. The broiler coil is directly under the metal cover, which in turn gets pretty hot and is used for roasting bread, or frying bacon ...
Ox tongue (cured and boiled) is easily available at any butcher. I do love it as waferthin slices piled on top of rye bread with some dijonnaise or sometimes horseradish mayo ...
