It's easy to expand content in your story by inserting new slides. You can do this from the Insert tab by selecting Insert Slide.
There will be several options; in each case click on the thumbnail image in the template, basic layouts, quizzing, screen recordings, or import to insert a slide into the project.
You have control over how this is inserted; into the current location in the current scene, in the same way as how it is set up in the template (it can be a single slide or a slide within a scene) or as a slide in a new scene in the existing project.
Here's a brief description of each Insert New Slide options: