This page means that your domain was successfully added to the hosting plan, points to Hostinger, and you can start developing your website.
Before that, just open Hosting → Manage → File Manager (either old or new one):
There, open public_html. Right-click on the default.php file (it should be the only file present) and choose Delete:
That's it! Now you can start a website hosting journey, for that you can either:
Create a migration request if your website is hosted elsewhere. Our team will gladly move your website for you!
You can also start developing a website on your own - for that, make sure to check a detailed overview of basic actions in File Manager