If you want to redirect a user at any time, just do the following
//open link in the same window Window.open("target.html", "_self", "");
That is useful, if it is the action that results from submitting a form or a result of an asynchron Service (RPC).
If you want to make a real html link, that is clickable, do this
//create a link Anchor a = new Anchor("Link text","target.html"); //place the link anywhere RootPanel.get().add(a);