Summary:
Additional information related to Customer, Jobs, employees, Vendors in QuickBooks may be required such as employee ID, email address, name of the supervisor, etc., may not be present in QuickBooks by default.These can be created as custom-fields which can be used to accommodate this information. 
These fields are similar to creating User Defined Fields in Web TimeSheet. Custom fields can be created from Edit Employee, Edit Customer or Edit Vendor screens.
 
Steps to create a custom field:
  • Go to Employee Center and double-click on the employee name, the Edit-Employee screen will be displayed.
  • Click on the Additional Info tab.  On the screen that appears, you will see Define Fields button.  Check the print-screen 'DefineFields.PNG' attached to this solution.
  • Clicking on the Define Fields button will display the screen that can be used to enter the name of the custom fields.
  • The custom field can be enabled for Customer:Jobs, Vendors, Employees at the same time or for one of them
Only text based information can be entered in these fields and these fields will then be available on the Additional Info tab when we try to edit an employee, Vendor, Customer or Jobs.
*Check the images for more information.