Drupal 8.x

I am getting the following error message while transferring  a Drupal 8.7 website to the root directory.  Could anyone oplease guide me on how to resolve this issue? Thank you so much for the great help the community members have extended to me so far and ciontinue to do so.

The website encountered an unexpected error. Please try again later.

Composer... Why, why, why... Okay, no whyning. Composer is the direction chosen by the powers that be. I try to use it. The past couple of days, however, typing this (on my localhost):

(....)\wamp\dru937>composer require 'drupal/entities_import:^1.2'

(as suggested by the makers on https://www.drupal.org/project/entities_import  ) leads to this:

Good morning,

One of my Drupal 8 websites was behaving properly until I started updating long-awaited modules. Once I tried to update a module it gave me an error message like the following. May I know how to handle this type of issue? Are there any standard processes to handle these types of errors?

The website encountered an unexpected error. Please try again later.

In my Bartik theme, there is a pencil icon, which leads to the contextual edit menu ("Configure block" / "Remove block" / "Edit menu" / ...). There are, however, a couple of problems with this icon. First, but let's skip this one, it's very ugly. 

Hello all,

I noticed that my font size is very small by default. It is not nice to read. How can I make the font size bigger so that you don't need a magnifying glass to read the texts?

Thank you for help!