C# interface vs extra variables code example

Example 1: creating interface in C#

using System;

namespace Grepper_Docs
{
    public interface IWhatever
    {
        bool doSomething(); //Interface methods don't have bodies or modifiers
    }
  
  	class Program : IWhatever
    {
        static void Main(string[] args)
        {
            var pro = new Program();
            pro.doSomething();
        }

        public bool doSomething() //methods must be public
        {
            return true;
        }
    }
}

Example 2: c# interfaces

public class Car : IEquatable<Car>
{
    public string Make {get; set;}
    public string Model { get; set; }
    public string Year { get; set; }

    // Implementation of IEquatable<T> interface
    public bool Equals(Car car)
    {
        return (this.Make, this.Model, this.Year) ==
            (car.Make, car.Model, car.Year);
    }
}