The Toolbox contains all the visual controls that you can put on your web page.  To add a new control, drag it from the Toolbox right onto your web page.  The Toolbox contains different categories of controls but the most common ones are placed in the category called Standard.  Note that in order to use the Toolbox, you must have the .aspx file open in the Code Editor.  If you have the .cs file open, you will notice that the Toolbox does not show any controls.  Click here to watch the video.