I feel now that I owe you some explanation of what is happening.  Clearly, you can see that in step 5 an anchor tag was created with a button click event that will call the JavaScript.  The important part is the passed parameter to that function (the standard control name).  That is how the function would know where to put the result when it finishes.  Now back to the function that is provided in step 7.  The function opens a popup window that displays the calendar WebForm called MyCal.aspx and allows the user to select his date.