There are literally hundreds of pasta recipes that involve tomatoes. This means that there are at least as many names for their sauces. With so many regions and dialects in Italy, and a global emigration, it should be no surprise that the many names for the sauces have been incorrectly altered or utilized. Here is some basic information for you.
In Italian, a basic tomato sauce is called a sugo al pomodoro or a salsa al pomodoro. The term marinara sauce is an incorrect term for this simple sauce, as a marinara sauce in Italy would include some sort of seafood. Nor is it correct to refer to a simple tomato sauce as a “gravy,” which would translate closer to a ragu, generally from Naples, in which some sort of meat is slowly cooked in the tomato sauce. (It’s technically not a gravy either, since gravy would be mostly meat drippings).
For the basic sauce, you can start with the core ingredients, tomato, onion, olive oil, salt and pepper and from there you can add additional ingredients. Basil is usually the first addition, and then other spices, carrots, celery, parsley, oregano, etc. and then of course, various meats. It all depends on your own tastes and traditions. Just note that the more you add, the less likely it is to be called a simple tomato sauce.
Any way you go, a tomato sauce can start with fresh or canned tomatoes, can be smooth or chunky and can be cooked for a long or short period of time. It all depends on your mood, the season and the amount of time you have.