I created a page “Blog” there the short descriptions of the entries (title, image, short description) are displayed correctly - looks all ok, but I have a problem with the creation of a Single Post page - nothing appears on it - a blank page. I chose the source: Blog post.
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you had set-up badly the route. Check example
Try it set-up like mine. You need it like /blog/url right?
Setup static page for /blog
Put inside the page a new detail page for dynamic source and change URL as on the screen.
Blog /blog - static page
Blog Detail /:blog
But you need to drag the page inside of /blog to have proper URL structure.
looks like its works now!, thank you!
szklarz.warszawa.pl/wpis-2
but I have another problem with “Rich Text” its doesnt show
I have “[object Object],[object Object]” instead of my content.
Do you bind properly Page > Data > Rich text?
Sorry cant help here 
need to wait for proper support from the DH in that case.
I need a help, dear @Pakic
aaaand another problem:
SEO meta-data (title, description) does not show up on the blog post page…
Are you trying to attach rich-text content from CMS to simple paragraph, or you are using actual rich-text in builder?
And for SEO, can you give me website url
You should be using rich-text element instead of paragraph when you are connecting content field from CMS.
And for SEO, you can right click > settings on blog single page, and then you have an option to connect dynamic fields for titles, descriptions, OG, etc.
ok, now its works!
But still problem with a seo - what I typed here doesn’t appear:
<title>szklarz.warszawa.pl</title> <- should be "Entry #2 Demo"
<meta property="og:title" content="szklarz.warszawa.pl" />
<meta name="twitter:title" content="szklarz.warszawa.pl" />
<!-- Description -->
<meta name="description" content="" /> <- blank
That fields from CMS are not automatically connected in the settings of a single page. We will work on that in future, now you need to manually connected them as on my previous screenshot/answer. 
Now everything is working. Thank you!