Questions about Apache Web Server Directories and IP Addresses

You would need to setup whats known as Virtual Hosts in your Apache config. There is a good walk through here for Ubuntu 16.04, The process is fairly similar in every distribution.

• https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-ubuntu-16-04

In the Create the First Virtual Host File section shows you how to set this up in the file /etc/apache2/sites-available/default.conf as shown below

<VirtualHost *:80>
    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/html
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

This example accepts all traffic for port 80 and sends it to /var/www/html. This includes all unassigned IP addresses and domains.

To add an assigned domain you would create a file /etc/apache2/sites-available/domain.com.conf and enter the below configuration.

<VirtualHost *:80>
    ServerAdmin admin@domain.com
    ServerName domain.com
    ServerAlias www.example.com
    DocumentRoot /var/www/domain.com/public_html
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

Repeating this for each domain/ip and adjusting the values in red.

You will following the remaining steps in the above link to enable these configurations.