예제 올려 드립니다.

여기에 코드를 입력해주세요public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // 화면 클리어
            this.Refresh();
        }

        // 마지막 마우스 클릭 위치
        Point m_LastPos = new Point(0, 0);

        // brush 생성
        System.Drawing.SolidBrush brushBlue = new System.Drawing.SolidBrush(System.Drawing.Color.Blue);
        
        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if ((e.Button & System.Windows.Forms.MouseButtons.Left) == System.Windows.Forms.MouseButtons.Left)
            {
                using (System.Drawing.Graphics oGraphics = this.CreateGraphics())
                {
                    if (m_LastPos != new Point(0, 0))
                    {
                        oGraphics.DrawLine(new Pen(Color.Blue), e.X, e.Y, m_LastPos.X, m_LastPos.Y);
                    }
                    oGraphics.FillEllipse(brushBlue, e.X, e.Y, 1, 1);
                    m_LastPos = e.Location;
                }
            }
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            m_LastPos = e.Location;
        }

        private void pictureBox1_Click(object sender, EventArgs e)
        {
            try
            {
                using (System.Diagnostics.Process p = System.Diagnostics.Process.Start(@"http://whiteat.com/WhiteAT_Csharp"))
                { }
            }
            catch { }
        }
    }