figura.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp39
{
    public class Figura
    {
        public int DlugoscBoku = 0;
        public string Kolor = "Zielony";

        public Figura(int dlugoscBoku, string kolor)
        {
            DlugoscBoku = dlugoscBoku;
            Kolor = kolor;
        }
    }
}
a potem w program .cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp39
{
    class Program
    {
        static void Main(string[] args)
        {
            Figura MojaFigura = new Figura(5, "żułty");
            Console.WriteLine(MojaFigura.DlugoscBoku);
            Console.WriteLine(MojaFigura.Kolor);
            Console.ReadLine();
        }
    }
}