以下在双斜杠后面的是我需要大家帮忙的地方:
namespace regions
{
    public class RegionsTest:System.Windows.Forms.From
    {
        void PaintREgions(Graphics g,CombineMode m,Point offset,string text)
        {
            Region ra,rb;//Region这个关键字是什么意思
            GraphicsPath p=new GraphicsPath();
            p.AddRectangle(new Rectangle(60,60,120,120));
            ra=new Region(p);
            p=new GraphicsPath();
            p.AddEllipse(0,0,120,120);
            rb=new Region(p);
            ra.Translate(offset.X,offset.Y);//Translate这句是什么意思?
            rb.Translate(offset.X,offset.Y);
            g.SetClip(ra,CombineMode.Replace);//SetClip是指什么呢?
            g.SetClip(rb,m);
            SolidBrush brush=new SolidBrush(Color.Black);
            g.FillRectangle (brush,this.ClientRectangle);
            g.ResetClip();
            //g.DrawString(text,new Font)
        }
    void OnPaint(object sender,PainEventArgs e)
{ 
  PaintRegions(e.Graphics,CombineMode.Union;new Point(0,0))//PaintRegions,与CombineMode是什么意思呢?
                        
   PaintRegions(e.Graphics,CombineMode.intersect;new Point(0,0)) ;

        PaintRegions(e.Graphics,CombineMode.Xor;new Point(0,0));
                                                                                                PaintRegions(e.Graphics,CombineMode.Complement;new Point(0,0))
                                                                    PaintRegions(e.Graphics,CombineMode.Exclude;new Point(0,0))
                                                                                                                                public RegionsTest()
        {
            this.PaintREgions+=new PaintEventHandler(onpaint);//PaintREgions这个关键字是什么?
            this.Size=new Size(800,800);
        }
        static void Main()
        {
            Application.Run(new RegionsTest());}
    }
}