As you didn't wrote which Numbers version you are using, I will respond upon Numbers '09
(1) As I wrote many times, the Help rely upon a list of indexed words. This list can't be infinite so we may easily be lost in searching something.
There are more efficient resources :
Numbers User Guide
iWork Formulas and Functions User Guide
cell AND border
would have returned :
in which I explained with screenshots what to do to set borders.
Yvan KOENIG (VALLAURIS, France) 9 mai 2011 21:11:37