1.  Download CKEditor 5 Dev Tools module: https://www.drupal.org/project/ckeditor5_dev 
2. Copy /ckeditor5_plugin_starter_template into a folder 
3. Rename and refactor to the code to match your chosen module name 
4.  Install Yarn brew install yarn 
5. Install node brew install node 
6.  Navigate to the root of new module folder and run yarn install 
7.  In the root run yarn build 
8.  clear cache 
9.  check that you have a new button avai

All information can be found in this article but in short:

1. Run composer create-project drupal/recommended-project my_site_name
2. Go to the new folder and install drush composer require drush/drush
3. Install manually or use drush: drush site:install