How do i draw rectangle inside picturebox control using Graphics class?

You could simply subclass the PictureBox class and use that.
An override on the OnPaint method should allow you to draw whatever you want.

Something like this should do the trick:

class CustomPictureBox : PictureBox
{
    protected override void OnPaint(PaintEventArgs pe)
    {
        base.OnPaint(pe);

        pe.Graphics.DrawRectangle(Pens.Aquamarine, new Rectangle(0, 0, 4, 4));
    }
}

Hope this helps,
Fredrik Bornander