CodeIgniter initial configuration

Hi, I'm from CI3 and I try to migrate on CI4.

I'm following this tutorial : https://codeigniter.com/user_guide/tutorial/index.html

Initial configuration is not clear. I do not understand what I should do to get a proper configuration of CodeIgniter. Here are some of my interrogations :

I read the CI_ENVIRONMENT variable can be set in the .htaccess file and in the .env file. Where should I put the configuration ?
I read the baseURL variable can be set in /Config/app.php, and in the .env file. Where should I configure baseURL ?
I read the database configuration can be set in the /Config/database.php and in the .env file. Where should I configure the DB ?

I try to configure  the DB in /Config/database.php and in the .env file, but I can't get ride of this error : 

You have not selected a database type to connect to.

You have not selected a database type to connect to.
I can't figure out how to properly configure CI4 for development on a local apache server and for production on a remote apache serveur. 

I read the doc dozen of times, but I still don't understand the configuration philosophy of CI4. Any light is welcome.