All components are shown in a hierarchical tree view within the Visuals tab of the Scene Manager. In this hierarchy, the top-level is made up of at least one scene. Scenes can't take the role of a child.
Components are always organized in parent and child components. A little triangle on the left side of a component indicates that the component is a parent component. Its child components are directly below it, slightly indented. Child components may themselves have their own children.
Clicking on the little triangle next to a component hides or shows its child components. You can change the hierarchy by dragging components to a different place. You can also color code components, and duplicate them. To do so, right-click an entry and select the corresponding option from the context menu.
Items in the Visuals tab have a visibility checkbox to their right. Activating it will make the corresponding component visible during playback, unchecking it will make it invisible. All components are initially visible, except in the case of multiple scenes of which only one can be visible at a time. You can manually change the visibility of components, and it also can be changed at playback time by means of actions and scripts.
Components with no visual representation (e.g. layers) still have a Visible checkbox in Scene Manager. This makes sense if the component is a parent of other components. In this case, changing the visibility of such components will also hide their child elements.