J3.x:Adding custom fields/User Field
From Joomla! Documentation
Articles in this Series
Provides a field to select a user from a modal list. This field displays the User Name and stores the User ID.
There are no special options within this field.
Creating the field
Let's say you create a field with the options shown in the next figure.
Using the field in the backend
In the backend while creating an article or a contact you see the field like in the following imageː
And if you click on it, a modal window will open and you can select an user in here.
Using the field in the frontend
In the frontend, you can see the field as you see in the following image. The option Automatic display is responsible for the position of the field and your template is responsible for the design of the field.
Fields are only displayed in the frontend if you have filled them with data in the article. If it is not a required field, can you forget it?