1. Set a featured image on each post, and at Customize > Content Options > Featured Images, place a check in the box labeled “Display on blog and archives.”
2. Don’t set featured images on posts, include at least one image in the content of each post, and at Customize > Content Options > Featured Images, place a check in the boxes labeled “Display on blog and archives” and “Automatically use first image in post.”
See the Blog page in the Dara demo. That’s the featured images appear on the blog page on this theme.
Can it be a vertical picture aligned on the left side of the blog excerpt?
Not on the blog page. You might be able to obtain this type of arrangement with display posts shortcode inserted into a static page, which you could then set as the static front page. See the following relevant support pages: