I just created a Laravel App (I'm completely new to Laravel and also don't have so much experience with Git(Hub)).
I created it locally on my computer with the
composer require "laravel/installer"
# Created by .ignore support plugin (hsz.mobi)
### Laravel template
# Laravel 4 specific
# Laravel 5 & Lumen specific
# Rocketeer PHP task runner and deployment package. https://github.com/rocketeers/rocketeer
### Composer template
# Commit your application's lock file http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file
# You may choose to ignore a library lock file http://getcomposer.org/doc/02-libraries.md#lock-file
As @TimL said in the comments this will be because you're
.env file won't have been set up. You're
.env-example is there for you to copy to make life easier.
You can either copy and paste it over, or if you using the command line:
cp .env-example .env
Then you populate it with the details for that environment.
Finally, to generate your application key just run the command:
php artisan key:generate
and this will generate the key for you.
The only other manual thing I can think of it creating the database before you use migrate.
Hope this helps!