Scrolling Positions is a feature of Gantry, which, when activated, modifies the behaviour of stacked modules. Instead of appearing vertically, the additional modules assigned to a given position become accessible via a javascript transition button, in this case: "More".
The Content Top and Content Bottom position rows have this feature.
In this demo, we have disabled the frontpage component from displaying, therefore, only modules will appear. This is achievable via a setting in Admin → Extensions → Template Manager → rt_nebulae_j15 → Advanced Disable Component : On/Off.
Additionally, you can disable the entire mainbody area with the Disable Mainbody setting.

Replicate the demo with ease with the RocketLauncher package, a full Joomla install, including the template, extensions and the sample data used on the demo. The Launcher is the perfect tool to understand the basics of the template.