CKEditor::textarea method not available

Hello,
I've downloaded CKEditor 3.6.3 and in the ckeditor.php file in editors root are folowing lines:

 Create CKEditor class instance and use one of available methods to insert CKEditor.
<?php
   $CKEditor = new CKEditor();
   echo $CKEditor->textarea("field1", "<p>Initial value.</p>");
?>