Here is an example for Apache to listen to any ip from port 80 for the name wiki.yourdomain.com. wiki.yourdomain.com could be something your type in to your web browser. The root directory of this virtual host is /var/www/YOURSITE.
<VirtualHost *:80>
DocumentRoot "/var/www/YOURSITE"
ServerName wiki.yourdomain.com
<Directory "/var/www/YOURSITE">
allow from all
Options None
Require all granted
</Directory>
</VirtualHost>
Add this code into your apache.conf file, or for some OS, save this code under /etc/apache2/sites-enabled/any_name_you_like.conf, and then restart the apache server.
To test if this is working:
systemctl status apache2.service in Ubuntu)sudo chown -R www-date:www-data /var/www/YOURSITE in Ubuntu 16.04)