The Posts menu option on the left is where you add blog posts. To add a new blog post, select the Posts > Add New option from the left hand WordPress menu.
You will then be able to set a title for the blog post, add the body content, and also provide all the meta information such as extra details and media. In the blog meta you can set the image for the thumbnail, and also the media type for the detail page.
You are be able to set a category and tag for your post so the archive page can search your post by category or tags with same value.