still assuming you have centos... the folder is called HOME and is located in the root of the server, you normally log in and end up in your user profile path, something like ~
Type cd /
the do a ls -l to show the folder
you can create inside HOME a folder for each site and use apache config to point to the folder(s) based on the domain
This tutorial shows you how to set up a new directory, how to grant the correct permissions, how to add content to a new page, how to turn on virtual hosting, and how to, if needed, set up local hosts. Virtual Hosts are used to run more than one domain off of a single IP address and allows you to run multiple sites off of a single DigitalOcean droplet. This tutorial describes how to set up virtual hosts with Apache on Centos
Failures to start are usually the result of some kind of misconfiguration. Check any changes you have made to the config file and ensure that they are correct. Check the apache error log to figure out what the problem is if you don't see any obvious problems in the config file. There should be an error message pointing you to the source of the problem.