Astra is a free WordPress theme. Therefore, it can be installed and used like any other.

To install it on your site kindly follow these steps:

1. Login to your WordPress Dashboard.
2. Go to Appearance > Themes > Add New
3. Search for - Astra
4. Install Astra
5. Activate it

Note: If you need the zip file of Astra theme, you can download it from the WordPress Repository here.