While updating a Nexus phone to Android 6.0 Marshmallow on Windows and Linux are trivial matters, things are a bit different for those who dwell in the land of the Macs. Thankfully there�s some help out there that should get you well on your way.
The video you see below was originally made for the Nexus 5�s Android 5.1.1 Lollipop, but thankfully it still fully applies to installing Android 6.0 Marshmallow on any modern Nexus device.
Otherwise, an attention to detail and the ability to sit through a 3 minute video are all you need to get yourself educated on what to do. Give it a go, but be careful. And remember, if you aren�t comfortable with manually flashing updates then there�s nothing wrong with waiting for it to hit your device naturally.