Well, for starters - if you have .env file with APP_NAME=Laravel - it will take that value and use it. If you were to change it there (actually you should change all possible values in .env file) - then it would change in your site.
As for the newname - this is a default value if .env file does not contain variable APP_NAME. If you would delete it from .env - it would take the second value.
Feel free to check: https://laravel.com/docs/5.5/helpers#method-env