dynamically add controls

Question

i try the code adding control at runtime.
firstly taken label,textbox & one button on .aspx file.then  add  placeholder to it. 
but when addstage button click so many time it may show that many time whatever on click .but it not show please guide me. and button 
(btn1)  which is created run time that not show anythink after click.
how to handle click event  at run time. please help me.