You can import an Asset Store package in the Package Manager window:
Open the Package Manager window and select My Assets from the Packages drop-down menu.
The list view displays any Asset Store packages that you have purchased.
If a large number of Asset Store packages appear in the My Assets list, you can search for a specific Asset Store package by name or version number.
Click the Download button if it’s enabled. If you haven’t downloaded the Asset Store package to this computer or device before, the Import button is disabled, and you need to download the Asset Store package first.
While the Asset Store package downloads to your computer, a progress bar appears beside the Import button. A Cancel button replaces the Download button you clicked.
下载完成后，__Import__ 按钮变为启用状态，__Download__ 按钮变为禁用状态。
Click the Import button to import the selected Asset Store package.
Import Unity Package 窗口将显示包中已选择的所有项，然后可以直接安装。
Unity puts the contents of the imported Asset Store package into the `Assets` folder, so that you can access them from your project window.