The additional tab got a major redesign from version 5.0 and contains now more fields, which were previously hidden in the default layout:
New additional tab layout
When clicking the buttons behind the dive center or trip fields, you can now open the details window to add or edit an item, or if an item is already selected, you can view some details right in a popup:
Trip popup and equipment list
The user defined fields control has been improved and you can now rename the field name directly in the control:
User defined fields
Tags: Logbook