How to create a child theme of an existing theme

Let's make a child theme of twentyten theme.The following steps are to be followed.........

1.Create a new folder under wp-content folder(where all other theme exist) and name it.Suppose we named it ChildofTT
2.Open any text editor(dreamweaver,notepad) and create a style.css file and save it in ChildofTT folder.
3.Add these code to style.css file

@import url('../twentyten/style.css');