If you have the above in your Apache configuration file and this is on a localhost, you would open a browser and enter:
and you would then see the index.html contents which usually show "IT WORKS". If you want learningnerd, you would create a directory under /var/www directory 'learningnerd' and then put files there (or you could put it in a sub-directory of lifelist) and then in the browser, type the path to it. Example:
I'm still not sure what you are looking for with 'change the text of the subdomain'?