how click event of these multiple button is generated.
When you create a button, add the event handler to it and then handle the same event in your page.
Button btn1 = new Button();
btn1.ID = "btnONE";
btn1.Text = "Press Me";
btn1.Click += new EventHandler(btn1_Click);
Somewhere in the same page:
void btn1_Click(object sender, EventArgs e)