How should I make a Plone content type with a downloadable File field?

I am trying to make a Plone content type with Archetypes that holds exactly two downloadable files as plone.app.blob.FileField. How do I make it so those fields can be tra开发者_Python百科versed to and then downloaded?

The spelling for the download URL is just content-item/at_download/field-name. The content type doesn't have to do anything special to support downloadable Blob fields.