Whats definition of 000-default.conf file?
Re: apache2 ubuntu
Your machine can host many different web sites, even with different addresses. Each web site is defined by its own configuration file. 000-default is a sample configuration to get you started with a single virtual host. Is that what you were wondering?
If you were to have a second web site on the same machine, you would just add a second configuration file pointing to a second DocumentRoot where the other web pages would be stored.