I installed the software via the automatic install.
Home automation is accessible via my browser. It sees my Philips Hue.
I now want to add my Zwave. Where do I find the configuration file configuration.yaml?
Tutorial: The Home Assistant configuration is located at /home/homeassistant/.homeassistant
How do I access that and how can I edit the files?
You can use Terminal on the Mac (or any third party SSH / Terminal program) and remote access your Pi. You could then use vi or nano to edit the config files.
Or you can set up a SAMBA share on the Pi, connect via SAMBA to your Pi and edit the files with an editor like Atom on the Mac.