When the account is entered into the system, extra fields must appear if the referral customer box is selected. If the box is not selected, the extra fields must not appear.
Note: By combining conditions and actions, you can do any of the following with business rules:
Set column values
Clear column values
Set column requirement levels
Show or hide columns
Enable or disable columns
Validate data and show error messages
Create business recommendations based on business intelligence.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/data-platform-create-business-rule