They're pretty simple. They're smallish (1") balls of ground meat, with a bit of onion, seasoned with salt and pepper and usually a warm spice, like allspice and/or nutmeg. They have a lot of breadcrumbs in them (preferably dry crumbs) and an egg or 2.
They are traditionally cooked in a cream sauce, which may be made with meat stock or not, a roux (flour and butter for thickening) or not, and cream.
This is a recipe that has been bastardized to death. Of course there are the canned cream of mushroom soup recipes, and there are also evaporated milk recipes, and stranger recipes where you are supposed to dump in various types of jam or preserves.
You serve your meatballs with noodles or potatoes of your choice, or rice. The important thing about being a good cook is to do the best with what you have. Here's how I would make them:
MEATBALLS:
1 1/2 lbs hamburger OR whatever ground meat you have
1/4 medium onion, chopped fine
2/3 cup breadcrumbs OR 1/2 cup oatmeal
3/4 tsp salt
1/2 tsp pepper
1/4 tsp allspice AND/OR 1/4 tsp nutmeg (you can substitute mace for the nutmeg, if that's what you have)
1 egg
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SAUCE:
2 cans (about 3 cups) of low-sodium broth (whatever you have)
1 tablespoon of butter or margarine
2 tablespoons flour
1/2 cup water
1/2 cup half-and-half, whole milk, evaporated milk, or 1/3 cup cream
Mix all the ingredients for the meatballs together: The meat, breadcrumbs, egg, salt, pepper, spices. Shape these into 1" balls, using a spoon or scoop. Now they need to be browned. You can do this by sauteing them in an oiled skillet, or if you want, you can put a sheet of foil on a cookie sheet, oil the foil, place the balls on the sheet, and bake at 400 deg for about 15-20 minutes, until the balls are brown.
Put the meatballs in a saucepan or in the skillet. Put in the broth and water. Cover the meatballs and simmer (low bubbling) for about 10 minutes.
In a separate covered container, mix the milk with the flour by shaking it together well until there are no lumps in the milk. Pour the milk mixture over the meatballs, add the butter, mix in well, and simmer another 10-15 minutes. Check seasoning of the sauce (I'd add some black pepper), and serve.
The reason my post is so long is because this is such a flexible recipe. Say you have cream of mushroom soup and you want to use it. Make the meatballs as above, then add the soup and 1 can of water, broth, or milk to the soup, mix together, cover and simmer 15-20 mins. Leave out the flour.
Say you have bouillon cubes, but no broth. Use enough cubes and water to equal about 3 c of broth.
Here's a recipe from food network TV that is pretty basic too: http://www.foodnetwork.com/food/recipes/recipe/0,1977,FOOD_9936_32087,00.html