First, configure your database, either by command line, or editing the "/config/databases.yml" file.
> php symfony configure:database "mysql:host=YOURHOST;dbname=YOURDBNAME" YOURDBUSER YOURDBPASS
Next, if you want to generate everything, forms, filters, models and data, run the following command:
For Doctrine ORM:
php symfony doctrine:build --all --and-load
For Propel ORM:
php symfony propel:build --all --and-load
This should get you up and running. You should definitely look at the tutorial for Jobeet posted on the Symfony Project website for more information on how this project works:
Doctrine: http://www.symfony-project.org/jobeet/1_4/Doctrine/en/
Propel: http://www.symfony-project.org/jobeet/1_4/Propel/en/