画填充圆：
Graphics gra = this.pictureBox1.CreateGraphics();
gra.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
Brush bush = new SolidBrush(Color.Green);//填充的颜色
gra.FillEllipse(bush, 10, 10, 100, 100);//画填充椭圆的方法，x坐标、y坐标、宽、高，如果是100，则半径为50
画圆圈：
Graphics gra = this.pictureBox1.CreateGraphics();
gra.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
Pen pen = new Pen(Color.Pink);//画笔颜色
gra.DrawEllipse(pen, 250, 10, 100, 100);//画椭圆的方法，x坐标、y坐标、宽、高，如果是100，则半径为50
写字：
Graphics gra = this.pictureBox1.CreateGraphics();
Font myFont = new Font("宋体", 60, FontStyle.Bold);
Brush bush = new SolidBrush(Color.Red);//填充的颜色
gra.DrawString("堵塞！", myFont, bush, 100, 100);