Scene Capture with a Mask?

Hello, may I request a Step By Step with screen grabs? I seem to be doing something wrong.

  1. I Google’d Post Process material. Made a Post Process volume and plugged it into the Rendering Features>Post Process Material Array.
    a. But all I see is the blue sky.
    b. Alternatively, if I plug the Post Process Material into the camera, I see “black” instead of sky.
    c. I do not know how to use the post process material as a stencil, either.

I truly hope you have some time for a Step by Step with screengrabs.