Factory is a Creational design pattern. Which is used to create different object on condition basis. You can make a method whose return type is an interface/base class and it take a parameter and on the basis of that the method will return object of any class which is implementing that interface. Example:-

 public interface IJunkFood {
 string Prepare();
 }
 public class Burger : IJunkFood
 {
 public string Prepare()
 {
 return "Burger is Ready";
 }
 }
 public class Pizza : IJunkFood
 {
 public string Prepare()
 {
 return "Pizza is Ready";
 }
 }
 public class OtherFood : IJunkFood
 {
 public string Prepare()
 {
 return "Other Junk Food is Ready";
 }
 }
 public IJunkFood GetJunkFood(string type) {
 if (type == "Burger")
 return new Burger();
 if (type == "Pizza")
 return new Pizza();
 else
 return new OtherFood();
 }
 String pizza = GetJunkFood("Pizza").Prepare();
 String burger = GetJunkFood("Burger").Prepare();