Storyboard scripting
An example of scripting in .osb.
In addition to using the Storyboard Editor(Design tab) to create Storyboards for maps, you can also use a plain text editor (such as Notepad or Notepad++). This is referred to as "Storyboarding by Scripting" (SBS), and allows you to be more precise (to the pixel and the millisecond) as to when sprites appear, what they do, and so on.
Beginner's guide
Doomsday has provided a nice beginner's tutorial to the concepts of SBS here (12:22).
Full specification
It is primarily based on the official specifications and experience in making large SBs. This is not a step-by-step guide, although simple examples are provided. It is meant to exhaustively detail how SBS translates into actions on-screen in osu!.
Please read the rule before doing SBS. It will save you the hassle later on. For sprite/object spec. and their moveset.
Note: Save on beatmap first before saving in Notepad. Also, the editor can be insensitive at times so save often.