using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {
           
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Pen pen = new Pen(Color.Red, 5);
            Point point1 = new Point(10, 50);
            Point point2 = new Point(100, 50);
            Graphics g = this.CreateGraphics();
            g.DrawLine(pen, point1, point2);
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;

            Pen pen = new Pen(Color.Red, 5);
            Point point1 = new Point(10, 50);
            Point point2 = new Point(100, 50);
          
            g.DrawLine(pen, point1, point2);
        }

        private void button1_Click_1(object sender, EventArgs e)
        {

        }
       
    }
}
 

if you run the program,you will get  the following window.