Unity Standard Assets and items on the Unity Asset Store are supplied in Asset packages. 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 is unpacked, as well as metadata about assets (such as import settings and links to other assets).
Starting from Unity 2020.1, the dedicated Asset Store window is no longer hosted inside the Unity Editor. However, you can still access the Asset Store website at https://assetstore.unity.com/ and you can still search for your purchased and downloaded Asset packages, as well as import and download them directly in the Package Manager window.
To purchase an Asset package from Unity or a third-party publisher, start by searching the Unity Asset Store to find Asset packages that meet your needs. When you find an Asset package you want to use, purchase or download it in the Asset Store. You can also make it easier to locate packages by organizing your assets with labels and hiding Asset packages that are deprecated or unused.
In the Unity Package Manager, select the My Assets filter to see your list of available Asset packages. You can search by name for Asset packages. When you find the Asset package you want to use, you can download and import it inside the Package Manager. If your Asset package has a newer version available, you can also update it directly in the Package Manager window.
To create your own (custom) Asset package, you can:
To import a local custom Asset package into your project:
You can use the Package Manager window to manage your Asset packages within your project. However, if you need to access your asset files directly, you can find them in the following paths:
~/Library/Unity/Asset Store
C:\Users\accountName\AppData\Roaming\Unity\Asset Store
These folders contain subfolders that correspond to particular Asset Store vendors and are available after download and import. The asset files are contained inside the subfolders using a structure defined by the Asset package publisher.