1) Click the Add Scene dropdown icon in the timeline.
2) Select Add Blank Scene.
3) Select Upload in the toolbar and choose the Import Files option.
4) After the upload is complete, drag and drop the imported asset onto the stage, the click the corners of the image to re-size.
5) Click away from the stage to see how the scene looks in final form. To use this background again in the same project, select Add Scene from step 1 and select Continue Scene, or use the copy and paste function after right-clicking on the scene.
6) Optional: right-click on the scene and select "Save as Template" to use this background in future projects.