You can add any custom field to your applications. Custom fields apply to all your applications.
Custom fields can be used for:
Filtering the Application table
Choosing visible columns on the application table
Adding form fields when sending a form on Workflows
Go to your Application Details tab on your settings page
Press the "+ Add field" button
The field you choose will be added to the same group of of fields where you are adding the field
Choose your field type
Follow the instructions for any of the application fields and press "Save"
Every application field needs to be in an application group. Learn how to add application details groups here