Question

I need help soon,
I tried to make paint using C#
It's not working

Graphics g;
Pen p = new Pen(Color.Black, 1);
Point sp = new Point(0, 0);
Point ep = new Point(0, 0);
int k = 0;
public Form1()
{
InitializeComponent();
}

private void red_Click(object sender, EventArgs e)
{
p.Color = red.BackColor;
default1.BackColor = red.BackColor;
}

private void green_Click(object sender, EventArgs e)
{
p.Color = green.BackColor;