Asset Store 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 Store package maintains its original directory structure and metadata about assets (such as import settings and links to other assets) when it’s unpacked.
To get an Asset Store package from Unity or a third-party publisher, start by searching the Unity Asset Store to find assets that meet your needs. When you find an Asset Store package you want to use, buy or download it in the Asset Store. You can also make it easier to locate Asset Store packages by organizing your assets with labels and hiding deprecated or unused packages. Refer to hiding Asset Store packages.
In the Unity Package Manager, select the My Assets context to view your list of available Asset Store packages. You can search by name for Asset Store packages. When you find the Asset Store package you want to use, you can download and import it using the Package Manager window. If your Asset Store package has a newer version available, you can also update it directly in the Package Manager window.
Unity users can become publishers on the Asset Store, and sell the content they have created. Follow the instructions in Publishing to the Asset Store for creating a package draft and uploading your assets for publication on the Unity Asset Store.
You can use the Package Manager window to manage your Asset Store packages within your project. However, if you need to access your asset files directly, you can find them in the Asset Store package cache. This cache, which is separate from the global cache, makes reusing and sharing packages more efficient. You can find the Asset Store package cache in the following paths (which might be within hidden folders depending on your computer settings):
~/Library/Unity/Asset Store-5.x
C:\Users\accountName\AppData\Roaming\Unity\Asset Store-5.x
~/.local/share/unity3d/Asset Store-5.x
These folders contain subfolders that correspond to particular Asset Store vendors and are available after download and import. The Package Manager stores asset files inside the subfolders using a structure defined by the Asset Store package publisher.
You can override the default location of the Asset Store package cache root. For information, refer to Customize the Asset Store cache location.