Text, images, videos and PDFs are treated as individual sections of content that you can move around in the story editor. When you first open it, you'll see the blank space prompting you to add a title and start writing the story.
To move sections of content such as text, images or PDFs, click on the section using the handle on the left side of the canvas and drag to move it.
Sections of text, videos or PDFs by default take up the entire width of the story editor. You can move them up and down but not left and right.
Image blocks can be moved around to be one across or two across. ie. they can take up the entire width of the story editor, or you can have two smaller images side by side.
To reorder images click on any image and drag it to where you want it to appear. If you drag it next to another image it will appear as a smaller image beside the other one. If you drag it onto its own line it will expand to fill the width of the story editor.