While passing Argument To Any Method Having ref and out keyword, In the following program we can see that while calling method math1 we have to initialized a variable as int b=0; and same while calling math2 it is optional to initialized a variable for passing argument.
lets see a small program.

 namespace OOPSProject
{
class Program
 {
//No Input & Output
 void Test1()
{
Console.WriteLine("First method");
}
//No Output has Input
 void Test2(int x)
{
Console.WriteLine("Second method: " + x);
}
//No Input has Output
 string Test3()
{
return "Third method";
}
//Has Input & Output
 string Test4(string name)
{
return "Hello " + name;
}
//Returning multiple values:
 int Math1(int x, int y, ref int z)
{
z = x * y;
return x + y;
}
int Math2(int x, int y, out int z)
{
z = x * y;
return x + y;
}
static void Main(string[] args)
{
Program p = new Program();
p.Test1(); p.Test2(100);
Console.WriteLine(p.Test3());
Console.WriteLine(p.Test4("Raju"));
int b = 0; //Initialization is mandatory
 int a = p.Math1(100, 50, ref b);
Console.WriteLine(a + " " + b);
int n; //Initialization is optional
 int m = p.Math2(100, 50, out n);
Console.WriteLine(m + " " + n);
Console.ReadLine();
}