Automatic blog page with custom design [closed]

First check your template or source code to find the classes added to the article as a whole (or any html element that wraps around the whole post. It probably looks a bit like this:

<article class="my-article">
<title class="my-title">TITLE</title>
<img src="https://wordpress.stackexchange.com/questions/228934/..." class="my-featured-image"/>
<div class="my-content">
POST TEXT
</div>
</article>

Now, in your style.css file you must distinguish between even and odd posts:

.my-article:nth-child(even) .my-featured-image (float:left;)
.my-article:nth-child(even) .my-content (float:right;)
.my-article:nth-child(odd) .my-featured-image (float:right;)
.my-article:nth-child(odd) .my-content (float:left;)

Beware that above is how you would normally switch around two items with css. This might interfere with how your theme uses its css. In stead of floats you could also use flexbox.