Put some olive oil in a non-stick frying pan, enough to cover the bottom of the pan, and fry the meatballs until they are brown all over. You don't have to use lots of oil - turn them over so that they cook on all sides, and make sure the heat isn't too strong, otherwise they might burn. You will probably need to fry them in two or three batches, depending on the size of your frying pan. As each batch is ready, put the meatballs straight into the pan with the sauce and when they are all done and in the pan, leave them to simmer in the sauce for about half an hour.