How to Create and Use Packages in Unity
How to create Packages in Unity :
How to import & Export Packages in Unity:
Package: reusable unity centric file
Package is a wrapper for assets and their respective metadata.
Note: Packages are created to reuse assets in many projects.
Select the Cube prefab (or Assets) - Assets menu - Export package... - Export - Name it - Save
Importing a package:
Create a new project - Assets menu - Import package - Custom package - Select the package to import - Open - Import