How to add text description to custom fields and custom Taxonomies?

How to add text description to custom fields and custom Taxonomies?
I see that for the Store Taxonomy, I can add text such as [STORE text=”More offers from”].
How can I add text to other custom fields and as well as custom Taxonomies?
For example, [custom_field_name text=”Text here”] and [CTAX key=Custom_Taxonomy text=”Text here”]