Hello Vitalie,
This looks like your webserver (Apache, from the screenshot you shared) is not configured: instead of passing the request to the application server, it just lists the files available in the root folder. See the alaveteli docs https://alaveteli.org/docs/installing/manual_install/#configure-the-web-server about how to configure it (you might need to go through the section above about configuring the application server as well).
In short, when someone visits your site from their browser, a request is sent to your webserver (apache here), which should pass that request to the application server (passenger or thin) which runs the alaveteli code. Once alaveteli has produced a response, that response data does the reverse trip back to your visitor. This is not happening in your screenshot.
Hope this helps,
Laurent / madada.fr