You can find this image in the sample data under Media in the Content menu item in the top menu of the Administrator Panel.
You can access the Administrator panel by using your login details sent to you in your welcome email.

Your home page is set to display the four most recent articles from the blog category in a column. Then there are links to the next two oldest articles. You can change those numbers by editing the content options settings in the blog tab in your site administrator. There is a link to your site administrator in the top menu.

If you want to have your blog post broken into two parts, an introduction and then a full length separate page, use the Read More button to insert a break.

On the full page you will see both the introductory content and the rest of the article. You can change the settings to hide the introduction if you want.