You will receive an order receipt email which contains a link to download the installer file. Make sure you download the installer onto the Windows or Mac device on which you intend to use the app. Then run the installer and the app will be installed.
It's not possible to share an app across platforms, e.g. the iPad app won't work on an android tablet, Windows PC or a Mac.
The good news is that it's possible to share apps with other people, within your household, using the same type of device: