I'd like to make a database, with doctrine, with an interface in PHP/Symfony2.
It's a company that sells clothing. So we have a table stock with product elements and a table Product with all clothes.
Could you guide me where to start ?
Here is a good start: http://tutorial.symblog.co.uk/
This tutorial shows you how to create a blog with Symfony, Doctrine and Twig. If you rename the Blog entity into Product and change it's properties to fit you product model you are good to go.
More on working with Doctrine in the official documentation here: http://doctrine-orm.readthedocs.org/en/latest/tutorials/getting-started.html