Laravel command not found?

Installed Apache, mysql, php7, just downloaded composer in a folder which did "domain" did the composer init. Now I want to install Laravel: Do

First, download the Laravel installer using Composer.

composer global require "laravel/installer"

Did, then:

laravel new blog

But Laravel says command not found, and the above written

Putting as the PATH the directory ~/.composer/vendor/bin, it will be possible using laravel.

How to specify PATH in Ubuntu 16 ?