Enumeration Explanation of {0}

I was wondering I've seen enumeration values accessed and output in two ways one was by array/element notation and the other which included {0}, {1} could someone give me a detailed explanation of this from the following code example.

I understand that there's some value swopping going on but I'm not sure I understand why.  I've search msdn but to no avail.

using System;
public class EnumTest 
{
    enum Days {Sat=1, Sun, Mon, Tue, Wed, Thu, Fri};
 
    static void Main() 
    {
        int x = (int)Days.Sun;
        int y = (int)Days.Fri;
        Console.WriteLine("Sun = {0}", x);
        Console.WriteLine("Fri = {0}", y);
    }
}

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