Is this a first stage of what will be a multi stage rocket?
This is a prototype of the bottom part of the second stage of a two stage rocket called Starship that will have more lifting capability than the Saturn V.
The second stage of Starship is about the same height as SpaceX’s Falcon 9 but a much wider diameter.
Here’s a video of the second stage orbital prototype being built in Cocoa, FL.
https://www.youtube.com/watch?v=A7N8DpB0HeQ
The shorter one will be stacked on the taller one to make the Starship which is only the second stage of the finished rocket.
No. It a test bed for the engine and the guidance control system and software for the thrust vectoring.