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