J3.x:Adding custom fields/What components are supporting custom fields
From Joomla! Documentation
Components supporting custom fields
Articles in this Series
What components are supporting custom fields
You can use custom fields in the article manager. Open the article manager from the menu in the backend via Content | Articles. In the left pane you will find the menu items for editing the custom fields. Alternatively you can edit custom fields for articles directly via the menu Content | Fields.
You can use custom fields for contacts. Open the contact manager from the menu in the backend via Components | Contacts. In the left pane you will find the menu items for editing the custom fields.
Through some plugin events 3rd party extension developers are able to easily integrate the custom fields feature into their components. It will look as part of their extension, similar to categories, tags or history.
However, the exact usage in this extension depends on the integration. Navigate to the next article to see how to integrate the custom fields to your component.