After you've created your narrative and uploaded assets, you're ready to use the composer.
For written description on the composer and how to use it, you can read the following:
The Composer allows producers to assemble their audio/video assets into linear or interactive experiences with spatial audio. Once you are satisfied with a Narrative’s composition, you can stage it to preview internally or publish to your app. The Composer is best used on laptop or PC with the latest version of Google Chrome.
You can navigate to the composer by clicking on one of your narratives in the CMS. This will take you to the narrative "Overview" page. From there, underneath your narrative thumbnail click on "Open Composer". Before opening the Composer, make sure you have already uploaded assets for your narrative.
On the composer, you build your content on the canvas. The canvas is navigated using controls at the top left of the composer, allowing you to zoom in and out. You can also navigate the canvas using the mini map at the bottom left, along with by clicking the hand on the top left, then dragging the canvas.
You'll find your uploaded video assets in the bottom left, under the video tray.
You'll have options for saving and staging at the top left under File, which will be covered in more depth in the Staging and Saving section of the support docs.