Check out example codes for "c# communicate with arduino". It will help you in understanding the concepts better.

Code Example 1

using System;
using System.IO.Ports;
using System.Threading;

namespace ConsoleApp1
{
    class Program
    {
        static SerialPort _serialPort;
        public static void Main()
        {
            _serialPort = new SerialPort();
            _serialPort.PortName = "COM4";//Set your board COM
            _serialPort.BaudRate = 9600;
            _serialPort.Open();
            while (true)
            {
                string a = _serialPort.ReadExisting();
                Console.WriteLine(a);
                Thread.Sleep(200);
            }
        }
    }
}

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