When you have selected to create a new field from the Custom Fields interface, the 'Add Field' box will open.
Enter the name of the field you wish to create in the 'Field Name' text box and select a type from the 'Data Type' box. Click 'Add' to add the field and return to the previous window.
After a new custom field has been created, it can be accessed by viewing the appropriate borrower, resource or tutor group record card and is generally found on the advanced tab.
You may need to close and reload your browser before any changes are reflected.