These are the official firmware on Android N provided by google.But it is still in the developer mode.Follow below steps on How to install android N on the nexus device.
#Download The firmware images from the link below!
1.Nexus 5X “bullhead”
7.Pixel C “ryu”
#How to install Android N Dev Preview
Download the appropriate firmware for your device.Then install it in your device by placing in your device internal memory and then navigate to Settings -> About -> Check System update.
You will get the notification of “A new System Update is available” Just tap on Install and wait for the process to complete.