They're easy peasy to make. Just mix up a pound of ground beef, 1/2 cup of bread crums, 1 egg, and 1 tablespoon italian seasoning. Then shape the mix into 12 meatballs. You also need 12 (1/2 inch) cubes of mozzarella cheese. Just press each cube into a meatball and enclose it.
Also need your favorite sauce here... bring your sauce to boil, and drop in the meatballs. drop the heat to low and simmer the meatballs for 20 minutes. Its best to put the cover over the top, or you'll make my mistake, and cover the stovetop and counter with bubbling sauce

Then pour over your spaghetti and serve.