Last week, Google surprised a number of us, and launched the Android N Developer Preview, well ahead of Google I/O - where this stuff normally happens. The Android N Developer Preview is a way for developers to get in on Android N before the public release and be sure that their apps and such are working with the update before it gets pushed out to everyone. Google has been doing this since the Android L announcement back in 2014. We'll see 5 developer previews this year, equating to about once a month leading up to the August/September release.
Many people have the Android N developer preview on their Nexus device already, simply because they want to play around with the new version of Android. And who can blame them? Now, Chainfire has released his first test build of SuperSU for the Android N developer preview, so that those with the preview on their Nexus or Pixel devices can get root access right away. With these being Nexus devices, root is always pretty simple to get. But Super User or SuperSU in this case, was not built for Android N, and the binaries for Android Marshmallow weren't working to well with the developer preview. But now you should be able to get some root access with this test build of SuperSU.
Using SuperSU is pretty simple, and if you know what SuperSU actually is then you should be good to go. But if you don't know what SuperSU is, then it's highly suggested to read up on it before using it on your device. As there is always the possibility of causing damage to your smartphone, tablet or even set-top box (in the Nexus Player). Which we won't be responsible for any damage done to your device. The Android N Developer Preview is being done via an over-the-air update, so you don't even need to flash the entire factory image. Making things much faster for everyone to get the update and play around with Android N. Internally, Google is calling this release "New York Cheesecake". It'll likely change before release in Q3, as it typically does. We're still holding out hope for Nutella.