You can complete assignment operations in the hierarchy using the Add buttons located on the Users, Vehicles, Drivers, and Roles hierarchy tabs. For example, to assign vehicles to a node in the hierarchy, click the Vehicles tab then click the Add Vehicles button.
In the dialog box that opens, select the vehicles you want to add (you can also use the filter tool located in the upper left corner of the dialog box to search for vehicles) then click the Add Vehicles button:
You can add drivers, users, vehicles and roles to hierarchy nodes in this way. Vehicles and drivers can only be assigned to nodes on the lowest level, but users and roles can be assigned to any node of the hierarchy.