Apple's devices are very easy to prepare, but it is required that you have access to the internet, either via Wifi, or via 4/5g on the phone. The guide deals with three scenarios, first-time setup for a new user, and two ways to transfer from an old iOS phone to a new one.
The setup assistant takes you through some mandatory and some optional settings. We do not describe all the choices here. You can skip many of the choices by pressing "Configure later". If you