That's a webserver configuration and has nothing to do with PHP (not meant as a flame, although it sounds a bit ilke it, sorry).
The webserver has to be enabled to see user directories. These are the web directories under the homedirectories of users on the system, typically a subfolder called public_html.
For instance:
http://www.bla.com/~flor
would serve
/home/flor/public_html/index.html