Get it:

$ curl -LsS http://symfony.com/installer -o ~/opt/symfony/symfony
$ chmod +x ~/opt/symfony/symfony

Create app:

$ symfony new my_project_name

Internal server:

$ php app/console server:run
$ php app/console server:start
$ php app/console server:stop

Check configuration:
http://localhost:8000/config.php

Check security:

$ php app/console security:check