What is the difference between these two methods? Using params or just doing everything in one class

public static void Main(string[] args) {
  int a = 2, b = 3;
  int sum = Add(a, b)
}

public static int Add(int a, int b) {
  return a + b;
}
//5 variables

public static void Main(string[] args) {
  int a = 2, b = 3;
  int sum = Add(a, b)
}

public static int Add(int a, int b) {
  return a + b;
}
//5 variables

public static void Main(string[] args) {
  int a = 2, b = 3;
  int sum = a + b;
}
//3 variables

public static void Main(string[] args) {
  int a = 2, b = 3;
  int sum = a + b;
}
//3 variables