Installing Drupal

While installing drupal 8 in local environment, I did not provide any DB details, so it created default settings.php and automatically created DB also. 

$databases['default']['default'] = array(
  'database' => "db",
  'username' => "db",
  'password' => "db",
  'host' => $host,
  'driver' => "mysql",
  'port' => $port,
  'prefix' => "",
);

I have been reading all the articles about how to use Composer to install 8.8 but I think I'm confused about where I should be running this from.

Busy with my drupal 7 to 8 migration on my local windows machine using Xamp php version 7.3 before bringing it to life this problem arises:

After migration was done and most of my content types with content are upgraded using the Gui way, to drupal 8 I started with installing a Theme.
I picked the Radix theme and tried to install it.
This requires components.

2 weeks ago stil on drupal 8.7.10 this installation works fine and I was at the stage to work on the layout of the site with this Radix theme.

I have been asked if can help on their drupal site as they got errors/warnings on it and can't see the site, I have never used drupal before but looking at the errors/warnings, I am wondering if the path is incorrect but can't see where to change the path, I found the settings.php but most of the code is commented out, I thought there may be some sort of config file that has the path in it

The errors/warnings on the site are below

Greetings,

I'm in the process of migrating a site to a new hosting server.  I don't have any problems moving the physical files or importing the database.  The problem is that the old server's webroot was /home/web and on the new server it's /user/public_html  I'm not sure where I might need to set or search/replace this path change in a Drupal site built via composer.  Any insight would be highly appreciated.

-Alec

Hi, I'm setting up a server for my own testing, it's a vps running windows, with a manual install of php, sql server etc

I can't seem to get past the first install page - where the language is selected, clicking 'save and continue' just loops me back to the same page - there are no errors that I can see.

Thought it might be more on the server or php config side rather than drupal side, so just installed wordpress as a test and it went in no problems.

Does anyone know what could cause this problem? have copied the default.settings.php to settings.php to no avail