How to Create and Use Packages in Unity

Notes:

How to create Packages in Unity :
How to import & Export Packages in Unity:

Assets: Packages
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.

Steps:
Creating package:
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