Newbie question: getting scaffolding to handle belongs_to relationships

Sorry in advance if this question is very simple. I was looking for
advice or a link to help with the following issue.

Let's say I have an app where I have categories of food like
'Meat','Dairy','Fruit' and the MVC functionality of this works well
already.

Now I create another sub-application where I add certain items of food
like 'Orange','Chicken','Milk', but I want to allow a user to pick
which category a particular item belongs to. Is there an automated way
of getting such an html select box with categories displayed?

BTW, I have successfully done this already, but I am afraid that I am
not harnessing the potential of RoR entirely here.

THANKS IN ADVANCE,
David

My sequence:
1. create tables
2. create models
3. create scaffolding
4. modify items_controller
5. modify _form.html for items to allow for an html select to be
created

Please offer any alternatives to what I have already done below:

tables= categories, items
--each have their own id
--items also has category_id