The HGV tab can be selected under each vehicle when the vehicle type is set up as a HGV vehicle (HGV vehicles are shown with 
on the left hand side).
Working your way through the HGV details area, you are able to determine the Operator Licence and Centre that is responsible for the vehicle
Within Configuration details you can determine the type of vehicle the HGV is, you are able to add trailer configuration etc.
The HGV area is a really good area on the software that allows you to store all of the important information about your vehicle for you and your colleagues.