Should the types that are built in to HiFi be insufficient, it is also possible to modify them with Custom Fields. Custom fields allow you to customize areas of your site with fields that would be helpful.
For example, if you are using HiFi to host a porfolio, it might be nice to create a Fieldset of "Project Type", "URL" and "Project Date" and apply it to your Portfolio section. These field would then be added to the Admin interface in that section and be available in the templates.
This is a great feature that makes it easy to customize HiFi for individual sites while keeping the interface as user-friendly as possible.