Yii2 php init command

Question

What does php init command actually do?

When I run this command in cmd after creating my project using this command: composer create-project --prefer-dist yiisoft/yii2-app-advanced advanced

I see many files generated in different locations like common, backend, frontend.

 `some@user:/var/www/html/yiiapp$ php init
  Yii Application Initialization Tool v1.0

  Which environment do you want the application to be initialized in?

[0] Development
 [1] Production

Your choice [0-1, or "q" to quit] 0

Initialize the application under 'Development' environment? [yes|no] yes

Start initialization ...

  exist common/config/main-local.php
        ...overwrite? [Yes|No|All|Quit] All
overwrite common/config/main-local.php
unchanged common/config/params-local.php
unchanged yii
overwrite backend/config/main-local.php
unchanged backend/config/params-local.php
unchanged backend/web/index-test.php
unchanged backend/web/index.php
unchanged api/web/index-test.php
unchanged api/web/index.php
overwrite frontend/config/main-local.php
unchanged frontend/config/params-local.php
unchanged frontend/web/index-test.php
unchanged frontend/web/index.php
unchanged console/config/main-local.php
unchanged console/config/params-local.php
 generate cookie validation key in backend/config/main-local.php
 generate cookie validation key in frontend/config/main-local.php
  chmod 0777 backend/runtime
  chmod 0777 backend/web/assets
  chmod 0777 frontend/runtime
  chmod 0777 frontend/web/assets
  chmod 0755 yii
  chmod 0755 tests/codeception/bin/yii

... initialization completed.`