For a long time I couldn't accept seafood at our table, but I changed my mind after a few attempts to cook it at home, from tested and fresh ingredients. The shells, or the mussels, were the hardest to approach because of my first experience - I bought them incorrectly, at home I realized they had a dubious smell and I threw them away. But in time I learned all the aspects, from buying to cleaning and cooking. Now we enjoy their wonderful taste periodically, with the whole family. This variant of mussels with tomato sauce, or Moules a la Provencale has been our favorite for a long time now.
In the Moules Marinier Recipe you can find many details about how to choose and clean the mussels. I will not repeat them all here. Just remember that from the moment you have the idea to cook shells, the first and most important step is to identify the right store from where to buy them. I definitely recommend a supermarket/hypermarket with a good fish department or the specialized stores for the restaurants, where delivery is constant and frequent. Make sure you smell them when you buy them - good shells have the smell of salty seawater, not the pungent smell of fish.
For this recipe, you have to prepare the tomato sauce in advance. I recommend choosing one of my recipes, the Classic Marinara Sauce, or the Marinara Sauce in my version. I make it during the tomato season, store in jars and I have it all year round. You can buy a good tomato sauce for pasta and pizza from the store, one which was tested and you like - in any case, not the normal tomato boullion!