A container is the first building block of an asset and is used to contain related nodes in your scene. A container is not visible in the main viewport, but you can select it from the Outliner, Hypergraph Connections editor, and Asset Editor.
In this case, all the fire truck components (including lights) are grouped together. This is important because you want the fire truck components to move together when animated. Thus, the fire truck group node is the central node to the container, and thus will become the container’s root node.
To create a container for the fire truck
Setting these options ensures that everything the firetruck needs to maintain its current appearance is packaged into the container.
Setting these two options automatically publishes Fire_truck_GRP as the container’s root node (thus allowing it to be a parent or child in a scene) and publishes its attributes to the container so that they can be tweaked from the container’s interface.