Save the given value in the notepad using Filestream concept in c#

If you mean to save the text in a Notepad file (i.e. a text file, or one that has the extension ".txt") then it is pretty simple:

Handle the Button Click event, and insert the following code:

File.WriteAllText(@"C:\Temp\MyFile.txt", myButton.Text);

You don't need to use a stream for something that simple!

Write this code at button click event.

StreamWriter s=new StreamWriter(Application.StartupPath+"my.txt");
            s.Write(textBox1.Text);
            s.Close();

You should have to include System.IO namespace to access the IO operaions.