We can simply deem a 3D label as a 3D object with pure text in the scene.
There are several property groups can be used to customize a 3D label: Appearance, 3D Layout, Text and Miscellaneous.
3D Layout: as a 3D object, the label has the typical properties for defining its position, rotation and scale. You can control corresponding properties just like a regular 3D object.
As a 3D label, it naturally gains the perspective effect just like the other 3D objects in the scene. Please see the different visual effects between a 3D label and a regular label:
3D labels don't have parents. So basically, it cannot move in accordance with a specific object by assigning a parent.