J3.x:Adding custom fields/Url Field
From Joomla! Documentation
Articles in this Series
Provides a URL text input field.
Special options within this field are:
The allowed schemes are HTTP, HTTPS, FTP, FTPS, MAILTO, URL and FILE. This custom field essentially is a text field with the type of url in the backend while creating an article or a contact or a third party component that supports custom fields. It is only possible to fill in a qualified url - that is one with a scheme and domain such as http://example.com. The url will be translated into punycode prior to saving. This assures that the url will work as intended regardless of environment.
Use this option to determine whether or not relative URLs are allowed.
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
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?