Columns in Document Library with Content Types

Normal procedure is exactly like Juan described.

But If you have already created the conten type first (withouth the columns) - and then created a word document by using that content type. And now you want to add the columns to that content type you can:

1) Create the columns

2) Assign those columns to the content type used

3) Update the word document to contain new column properties by "Edit properties" functionality

4) There might be that the coulmns don't show up to the current view automatically (ether they are showing in edit properties) in this case, just edit the view and add the columns just created to the current view

hope this helps