how i can , Form the [Serializable()] ?

[Serializable]
public class Element
{
 public int field1;
 public string field2;

 public Element()
 {
 }

 public Element(int f1, string f2)
 {
   field1 = f1;
   field2 = f2;
 } 
}

static void Serialize() 
{

  FileStream fs = new FileStream("DataFile.dat", FileMode.Create);
  List<element> elements = new List<element>();
  
  elements.Add(new Element(1,"One"));
  elements.Add(new Element(2,"Two"));

  // Construct a BinaryFormatter and use it to 
  // serialize the data to the stream.
  BinaryFormatter formatter = new BinaryFormatter();
  try 
  {
    formatter.Serialize(fs, elements);
  }
  catch (SerializationException e) 
  {
    Console.WriteLine("Failed to serialize. Reason: " + e.Message);
    throw;
  }
  finally 
  {
    fs.Close();
  }
}