Welcome to the RealSense community!
The link below will take you to a hub-page for the 400 Series cameras, where you can access software, discussion papers and firmware driver links.
And here is the documentation hub page. Scroll down past the file list to find a variety of useful documentation links.
Example programs for the SDK are here:
In regard to Unity, the SDK's Unity wrapper comes with some example programs.
These samples are described on the Unity wrapper's front page. under the headline 'Step 2 - Open A Unity Scene'.
The Nuitrack SDK remains probably the easiest skeletal tracking solution for the 400 Series cameras.
Intel published some guidelines for implementing hand tracking, though they came out just before the 400 Series was released, so it's not clear how well it works on the new cameras.
You can get a good overview of the third-party tools compatible with the 400 Series on the page below:
Intel are also adding compatibility with further third-party platforms, which will increase the number of options for integrating modules into projects.