ICANN our standard installation makes use of a public folder, which is a common standard in modern applications to protect files (by not having storage under the webroot, it cannot be accidentally exposed)
This part of the instructions explains how to update your configuration to use this folder:
While this command is running, you can configure your web server. You will need to make sure your webroot is set to /path/to/your/forum/public, and set up URL Rewriting as per the instructions below
Most managed hostings actually have a text field in their web interfaces to enter the path to the webroot. If you don't use a managed hosting, it's the DocumentRoot property in Apache or root directive in Nginx that you need to customize.
If you don't want to or cannot use the public folder strategy, there is a section lower in the install guide that explains how to moves files to get rid of the public folder https://docs.flarum.org/install.html#customizing-paths
