Display 2nd selectbox

I am very new to scripting and appreciate any help from you gurus...
I have two selectboxes, (2nd select box should not be visisble)after
selecting an option in one selectbox the other selectbox should be
displayed.
I know how to do this is javascript, but not in ruby on rails because
I am not able to pick the proerties like style and nam for the select
box
Thank you