Hi @dani-gerber,
You have to set Featured Image on every post then only those featured Image will be shown on templates.
To set Featured Image on every post go to the page/post editor of every post and page. You will find ‘Featured Image
tab on right side from where you can set your desired image.
You can check our Home Page(Front Page Template) set up tutorial (here). It will help you to set Front Page template.
Or you can check our documentation (here).
Thanks
.
.