This is the default web page for this server.
The web server software is running but no content has been added, yet.
The administrator installed the web server but has not yet placed any site files into the document root for this host. Until that happens, every request that reaches this server returns the same default page you are reading right now.
The page is intentionally plain. It serves only to confirm that the server is reachable, that the network path is open, and that the daemon is alive enough to send back HTML over the wire.
Place your site files in the document root (commonly /var/www/html on Debian and Ubuntu, or /srv/http on Arch) and they will be served instead of this page on the next request. No restart of the server is required.
If you want to host more than one site on this machine, configure name-based virtual hosts. Each virtual host points to its own document root and listens for requests directed at a specific hostname. The match happens by inspecting the Host header that the browser sends with every request.
Once the real site is deployed, this page is overwritten by your own index.html and the visitor will no longer see this notice.