Tutorials:Working With StepMania 5/Before You Begin

Structure
StepMania 5 does away with some folders, as well as introduces some. In a nutshell:
 * There is no /Numbers folder. It has been replaced entirely with /Fonts.
 * Each Screen has 4 BGAnimation layers: Screen background, Screen underlay, Screen overlay, Screen decorations:
 * Background is the same as it is in 3.9 and above
 * Underlay appears over Background, but under the screen items and the overlay
 * Overlay appears over screen items and every other item.
 * Decorations add the bganimation to part of the screen, making them screen items.
 * Most internal classes have now been removed by default and must be added by hand
 * However this will not be a problem as we will walk you through adding these items back.

Interals

 * Many debug keys have been replaced with a debug menu ( F3 )
 * Additional support has been added for many other gametypes and features from other games