Custom Field Sets allow you to Group your various Custom Fields into separate headings. This is especially helpful if you have a large number of Custom Fields.
Once you add Custom Fields to a set, they will be shown under the relevant set in the Booking Summary.
Add & Manage Custom Field Sets
Go to Settings in the left-hand sidebar
Click on Fields
Click on Custom Fields
Click on the Event Temple area the Custom Fields belongs to (eg Booking)
Click New Custom Field
Click on the bottom picklist that says Custom Field Sets
From here you can Add New Custom Field Sets
Add in Custom Field Set Name and click Create
Or Edit (Pencil Icon) and Delete (Trash Icon) existing one
Additional Information
Currently, it is not possible to change the order of Custom Field Sets once they have been created. They will appear in the order they were added.