This guide it's valid for the Linux packages only. On Windows it's strongly discouraged to install apps. If you need to install an app and have Windows, contact us for a package changing.
Before installing Joomla:
Create the database by clicking on the right top on "Database" and then on "Create database".
(Click on the images to zoom)
Fill the spaces as in the example (write down the access data).
Now click on "Apps" > "All the apps".
Search "Joomla", on the right top click on the arrow to open the menu, then click on "Install (Custom)".
Fill the spaces as in the example (with your data) and click on "Install".
If all went good, you should see a window like this.