Intro to ArcGIS SceneViewer
The SceneViewer application in the ArcGIS Platform is very similar to the MapViewer.
However, the SceneViewer is designed specifically to set up your Scenes for use in your applications. The workflow is that you would author your WebScenes in ArcGIS Pro and publish those scenes to your ArcGIS Online account. You can then use the SceneViewer to mix and match those scenes as you see fit.
The MapViewer is still the central location you would edit your data and perform analyses.
The SceneViewer is specifically for laying out your scenes and slides.
I hope you enjoy this quick intro to the ArcGIS SceneViewer and try on your to create some interesting scenes for your application!