Now you are probably thinking, "Okay, which one should I use?" There isn't a general rule for this. Arrays and List<T> can serve the same purpose. You can find a lot of additional information online to convince you to use one or the other.
Arrays are generally faster. For what we are doing at this stage, we don't need to worry about processing speeds. Some time from now, however, you might need a bit more speed if your game slows down, so this is good to remember.
List<T> offers great flexibility. You don't need to know the size of the list during declaration. There is a massive list of out-of-the-box operations that you can use with List, so it is my recommendation. Array is faster, List<T> is more flexible.