noob with XBMC

Usually use Plex but this latest version is proving flaky. Keeps crashing and having to reinstall it all the time. Was rock solid on 4.4. ATV2. So am looking at XBMC instead. Plex was easy to setup as it had a Media Server on my Mac and found that automatically with the folders I use on my External drives for movie and TV plus iTunes and iPhoto was automatic. I cannot work out how you find your folders on your Mac. Is there a guide somewhere for doing this on the ATV2?