Stream myStream ; 
SaveFileDialog saveFileDialog1 = new SaveFileDialog(); 

saveFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*" ; 
saveFileDialog1.FilterIndex = 2 ; 
saveFileDialog1.RestoreDirectory = true ; 

if(saveFileDialog1.ShowDialog() == DialogResult.OK) 
{ 
            if((myStream = saveFileDialog1.OpenFile()) != null) 
            { 
                        StreamWriter wText =new StreamWriter(myStream); 
                         
                        wText.Write(" your text"); 

                        myStream.Close(); 
            } 
}