This is an extra section of content that can be added to the middle of your page. In order to add this, first go to Content Editor > page name > Page Properties > Page Layout > Custom Page. (This will allow the extra page elements to appear.)
To start adding your additional content go to Content Editor > Content Blocks > Add A Content Block > select the 'Group' of 'Image Content Section'. You can then upload your background image, add any content, and even add a button if you'd like! After saving, select the page/s you want it to appear on! Tada!