Showcase.yaml with images selector

Hi guys, I am trying to add an image field inside showcase.yaml in order to have sort of images linked with sections of the website. I am using the antimatter theme and I have added a few lines inside showcase which now gives me the select field. I am trying to make a 3 columns wide section with 3 images, text under them and button under the text with links to the sections.
Maybe I am doing something wrong but I guess I have to link the .yaml with the twig ? any ideas ? thanks in advance

I have managed to use the pagemediaselect and got a chance to select the image. now its time to find a way to creat columns with images, text and the buttons ...