But I'm can't type vietnamese, please help me!!!!!!
im-config in a terminal, then continue until you can select the ibus option. (this will allow to use ibus as imput method). when finished, add
ibus-daemon -drx to startup applications then restart your session and you should be able to use all the configuration you have made about ibus.
i recomend you to disable the app-laucher shortcut in order to use the switching shortcut for ibus.