1. Backup files: Compress the directory that contains our 'CORE' directory (typically 'public_html' ) and download it to local directory
2. Backup DB: GO to phpMyAdmin choose the relevant DB, click 'export' on the top right horizontal menu. use 'custom' to compress it or just click 'go' to download it as it is. save it to the same directory you saved the compressed file system
3. Put site in maintenance mode Configuration > Development > Maintenance mode

I used this youtube tutorial: https://youtu.be/QbLIDireUSg

Important notes:
Cahnge settings.php permissions from 444 to 777 before making changes (and then change back)

set the data base name, data base user and data base user's password

1. install devel module and enables its sub module kint.

https://youtu.be/Us1IKWfYscA

Drupal 8 Block Plugin API: How to create a custom block in drupal 8
Theme Inheritance: Creating a Drupal 8 sub-theme, or sub-theme of sub-theme

Twig Template naming conventions
The original template (twig) files, are in: core/modules or core/themes/classy/templates