The User Defined Fields are custom fields that, if the check box to the right is checked, will appear on your customer details screens. You can name the field whatever you want in order to track things that are not already included in the customer database.  

Note: You also have the option to print these messages on the ticket.

To configure the user defined fields, navigate to Manager Home > Config > Customers > Customer Setup.

To add a user defined field to the customer profiles click the checkbox on the right side of the field. If you want the field to print on the customer ticket then also click the box next to "Print".

Note: You must also configure your printer ticket to include customer data if you want this to print.

Once you have activated the field, you will be able to name the field.

If you do not activate the field, it will not show on the customer profile.

Be sure to save your changes.

You will see the fields in the customer profile on the front end as such.

And the back end customer profile will display as this.