Unfortunately all stuff surrounding server setup require a minimum knowledge of terminal command code setup. But you can find everything on the internet. There are even YouTube videos that explain stuff and there are plenty of help pages/documentation.
I guess you would just need to check if the index.html file with your contents actually saved and make sure you restarted Apache after the previous steps which may have involved changing the Apache config with a different document root.
To let PHP and MySQL talk to eachother, I use this:
mkdir mysql under /var and go inside it with cd /var/mysql
ln -s /tmp/mysql.sock mysql.sock
I guess for XenForo you can then run the requirements.php file and test mysql to see if you can use it.
You probably need to edit httpd.conf and enable things like rewritemod.
LoadModule rewrite_module libexec/apache2/mod_rewrite.so
Anyway, once it's all working, before installing xenforo, setup a virtual host for your test site first.
Maybe add easier management things like phpmyadmin