Add new entity in sylius 1.2.12



I am beginner in sylius and symfony and since a week, I can not add a new entity
I have already installed sylius and I would like to create a new entity contact, Slider, … which allows me to enter the contact data / images sliders in the BO and display them on the homepage of the frontend

j’ai suivi la documentation

mais ca marche pas.

i need your help.