Asset packages are collections of files and data from Unity projects, or elements of projects, which Unity compresses and stores in one file with the .unitypackage extension. Like a zip file, an asset package maintains its original directory structure when it’s unpacked. An an asset package also has metadata about assets, such as import settings and links to other assets.
To create your own custom asset package, use the Assets > Export Package menu option to compress a collection of assets in your current Unity project. For more information, refer to Creating your own Asset packages.
To import a local custom asset package into your project, use the Assets > Import Package menu option to unpack the collection into your currently open Unity project. For more information, refer to Importing Asset packages.
To remove a local custom asset package from your project, use the Project window. For more information, refer to Removing local asset packages.