Explaining how to design a database to model the stocks of a firm to my Grand'ma
You might find this page interesting. Your schema seems to be reasonable - the only way you'll know is by writing your application and seeing if it works :-).  

What you initially call a "bon de commande", you later refer to as a "bon de livraison" (which makes more sense in French). You also fail to provide a definition of ContenuBL (La composistion d'un bon de livraison je présume?).

Most of the people on this forum won't be able to speak/read French and will find it difficult to answer the question. If you like, I can translate it into English for you?