When you login to your controlpanel (usually yourdomain:2222), you can access the Installatron website application installer by navigating to Extra Features > Installatron Script Installer.
From here you can choose an application from the grid view, when you click on a image of a product you get an overview of the application and in your top right corner you got a button named
”+ install this application”
This will start the installation of the application to your account.