I get a error when I try install auto-complete in emacs

I'm newbie in emacs...I've a few days and I think emacs is awesome but I get a error when I try install auto-complete...I install it from http://cx4a.org/software/auto-complete/ the installation works (I use the makefile)...but when I put this lines inside my emacs.d

(add-to-list 'ac-dictionary-directories "~/.emacs.d/ac-dict")
(require 'auto-complete-config)
(ac-config-default)

I get this error

Warning (initialization): An error occurred while loading `/home/yo/.emacs':

Symbol's value as variable is void: ac-dictionary-directories

To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file.  Start Emacs with
the `--debug-init' option to view a complete error backtrace

I've my folder .emacs in /home/yo/.emacs and inside this I've the folder ac-dic..inside this there are c++ mode..lisp mode ruby mode...etc..etc...etc.....

my autocomplete.el is inside my .emacs too...what am I doing wrong??...thanks!!!