well the "Console.WriteLine" method you are using actually takes all of the arguments you pass it (other than the format string) and puts them all into an array. Arrays are just a collection of items. Each item in an array can be individually referenced using an index, but in .net world the indexes start with 0 instead of 1. This is common in most languages because 0 is actually the lowest non-negative number, not 1.

So let's say you were writing the Console.WriteLine method it would look something resembling this...

public static void WriteLine(string format, params object[] args)
{
    // the "params" keyword allows all parameters to be inserted
    // into an array. This allows a variable number of arguments
    // to be handled by a single method definition.

    // So here we have the args array that contains each of the items
    // you want inserted into your console output.

    // We are going to loop through each of the objects passed and replace
    // its respective index reference in the format string.

    for (int i = 0; i < args.Length; i++)
    {
        // This is what we will be replacing in the string - e.g. {0}, {1}, etc...
        string indexRef = "{" + i.ToString() + "}";

        // This is what we will be replacing it with...
        string indexItem = args[i].ToString();

        format = format.Replace(indexRef, indexItem);
    }

    // Great - now that all of the items in the "args" array have been
    // inserted, we can print the finished string to the console...
    WriteLine(format);
}