You are basically supplying our own implimentations for these operators (=, -, !, ~, ++, --, true, false, *, /, %, &, |, ^, ==, !=)(the only difference is that if you overload << you have to overload >>)when used with specific parameter types. It's exactly as when you overload methods by supplying different parameters for methods with the same name.

For example:

public class AddClass1
{
   public int val;
   
   public static AddClass3 operator +(AddClass1 op1, AddClass1 op2)
   {
      AddClass1 returnVal = new AddClass1();
      returnVal.val = op1.val + op2.val;
      return returnVal;
   }
}

In this case you can make a call like the following:

AddClass1 op3 = op1 + op2;