@yWalker

This is very easy using apache virtual hosts

Follow these instructions to achieve what you want

• Copy the default apache site and give it another name using this command: sudo cp /etc/apache2/siates-available/000-default.conf /etc/apache2/sites-available/domain1.com.conf
• Modify the default configuration by changing the following options:
  • ServerName domain1.com
  • ErrorLog ${APACHE_LOG_DIR}/domain1.com_error.log
  • DocumentRoot /var/www/html/
  • CustomLog ${APACHE_LOG_DIR}/domain1.com_access.log combined
• Repeat step one and name the file as domain2.com.conf
• Repeat step two and replace domain1.com with domain2.com also do not forget to change DocumentRoot to /var/www/html/admin
• Enable the two new sites with these two command: sudo a2ensite domain1.com.conf, domain2.com.conf.
• Restart apache with this command sudo service apache2 restart

Now you can use domain1.com to access the site at /var/www/html and domain2.com to access the site at /var/www/html/admin

Hope this helps, revert back here for any further questions.

What is your webserver of choice.

I personally use NGINX.

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