The first thing you need to do is add the Blog posts element in the place where you want the posts listed.
Then click on the home menu ...
... and select "Blog" and then "Posts".
Click the plus button to create your first blog post.
You can click on the title to change it.
Use the plus button to add content elements. It works just like adding element in a page.
When you are ready to publish your post click on the title menu and select Publish.