Field tag gets a field value from the current item in the loop.
If there's no loop, it gets the field from the current post or page.
The field name is passed as the first attribute, or by attribute
<Field title /> <Field name=author_id />
Loop tag and each loop type's reference page for a list of available fields.
Loop type shortcut
type attribute with
name to get a field from a specific post.
<Field title type=page name=example />