Looking for help with instructions for installing Oculus Platform SDK for Unity.

Hi,

I am having an issue getting Unity to recognize Oculus libraries (or perhaps having an issue getting these libraries installed, I'm not certain).
For some background:

I have successfully installed the OculusUtilities package in my Unity project which has given me access to expected scripts, models, etc... Once installed this gave me the ability to apply C# "using" directive and include OVR related libraries installed with OculusUtilities.

However I'm struggling with the Platform SDK and hoping to find guidance. I'm trying to replicate the Leaderboard sample found in Oculus Dev docs here: https://developer.oculus.com/documentation/platform/latest/concepts/dg-cc-leaderboards/
If I try this 

 using System.Collections.Generic;
using Oculus.Platform;
using Oculus.Platform.Models;

// Coordinates updating leaderboard scores and polling for leaderboard updates.
public class LeaderboardManager
{ ...

The "using" directive has no idea where to find Oculus.Platform or Oculus.Platform.Models. I get a compiler error. I've downloaded the Platform SDK and see that there are various libraries for Android, etc.. I'm not sure what parts of the Platform SDK need to be installed in Unity or where in my unity project these specific files need to be installed to give me access to the Oculus namespace.

So I guess I'm looking for the correct procedure to install this library or a link to some documentation on how to do it. I imagine it's something simple I am missing, but again, using the OculusUtilities package was very straightforward and I was expecting the "Oculus" related namespace/libraries to be included as part of that but apparently it is separate.

Thanks!