Please tell me how to start & what should i include in my survival game project

I am an intermediate in unity.
I am just starting my new survival game project but i dont know where to begin with. i just want to ask what an survival game includes i know about RUST, THE FOREST… but from where they started.
Thank you very much in advance.

They started from the bottom. They created or used an available terrain engine, created a character controller, created an inventory system, day night cycle… so on and so forth until eventually it became what it is today.

There is no straight answer to give you besides to start looking into either coding or finding assets to fill those basic needs, and start making models, textures, and code to glue it all together.