Custom Type ArrayList with IEnumerator

See .net fiddle link https://dotnetfiddle.net/E4eCWl

I have a homework assignment to use an ArrayList of type Book so while I know List<T> would be the correct way to handle the issue I need to use an ArrayList as that is part of the assignment

so used

var books = new ArrayList<Book> {new Book("Moby Dick", 254)};

So bare with me here, my understanding here is that the once I add the custom type Book to the Arraylist I am creating a custom class as Resharper has helped me create a new class to accommodate the adding of the book, so a new class has been added, but now I am stuck, as I have no idea on how to implement the Add method or what to use the GetEnumerator for..

Any tips or website I can go to to help me further or have I gone down the wrong path to begin with on creating the type.

Custom Book Class

class Book
{
    public string Title { get; set; }
    public int NumberOfPages { get; set; }

    public Book(string title, int pages)
    {
        Title = title;
        NumberOfPages = pages;
    }

}

Generated Class

class ArrayList<T> : IEnumerable
{
    internal void Add(Book book)
    {
        throw new NotImplementedException();
    }

    public IEnumerator GetEnumerator()
    {
        throw new NotImplementedException();
    }
}