public interface IUser { void AddUser(string name, string email, string password); } public class User : IUser { public void AddUser(string name, string email, string password) { // code to add user to database or user storage system } } // example usage: User user = new User(); user.AddUser("John Smith", "[email protected]", "password123");In this example, we define an interface called IUser that specifies the AddUser method. Then, we implement that interface in a class called User. Finally, we create an instance of the User class and use the AddUser method to add a new user to the system. Package Library: The package library for this method might be a user management or authentication library, such as Microsoft's Identity framework or SimpleMembership. These libraries provide pre-built functionality for adding, managing, and authenticating user accounts in a web or application environment.