Use prefabs (prefabricated templates) to create reusable content in your project.
For example, use prefabs to:
See Creating and editing prefabs.
To instantiate prefabs in your project, use prefab placeholders. When prefab is instantiated, the content of the prefab replaces the placeholder. The properties you set for the prefab placeholder are added to and override the properties defined in the root object of the prefab. See Using object prefab placeholders and Using layer prefab placeholders.
In your project you can treat a layer prefab placeholder as any other layer, and an object prefab placeholder as any other object with any number of children configured in any kind of a sub-tree. In the project, the placeholders instantiate an exact copy of that prefab.
Using layer prefab placeholders