Impossible installation

Have you installed server and PHP?
Apache or Nginx and PHP

I installed Apache2, PHP and mariadb and I configured a lamp server.
I have also configured Apache2 and mariadb.
After I downloaded the last version of wordpress that I place in /var/www/html and I modified the permissions of Apache webroot.

where I can install wordpress but a page filled with php code.

Just PHP code or some kind of error message?

Please provide more info.

Have you tested that PHP is working? A page filled with PHP code is due to PHP not being installed correctly, therefore not being interpreted by the server.

This is how to test PHP on Debian: https://wiki.debian.org/LaMp#Test_PHP

You should create a php.info page to get the information about your system and if it doesn’t run then you probably have a problem with php running. Create a page called “pageinfo.php” in it paste this code

<?php

// Show all information, defaults to INFO_ALL
phpinfo();

?>

upload it to the home directory and then go to that page in your browser and you will see everything you need about php on your system.
Here is a link to more information

https://mediatemple.net/community/products/dv/204643880/how-can-i-create-a-phpinfo.php-page