The Step Editor is a graphical editor that can be used to create or edit MIDI note and controller data. You can use the Step Editor to view and edit different MIDI event types, shown as vertical beams—or steps—along a timeline within a region.
Step: Each beam, called a step, represents a MIDI event. The value of the event is denoted by the beam height, providing an at-a-glance view of one or more different events and their values. For more information, see Create steps in the Step Editor and Change step values in the Step Editor.
Lane: Each MIDI event type, be it a note or MIDI controller, is arranged from top to bottom in horizontal lanes much like the track lanes shown in the Tracks area. The type of event shown, and controlled, on each lane is freely configurable. You do this by setting Lane parameters (for each lane) in the inspector. For more information, see Lane parameters overview.
Lane inspector: Use to alter the settings of the selected lane. For more information, see Use the Lane inspector.
Lane Set pop-up menu: You can save groups of lanes (several lanes that you have defined) as Lane Sets. You access these from the Lane Set pop-up menu in the inspector. For more information, see Use Lane Sets.
Click the Editors button 
in the control bar, then click the Step Editor button.
Do one of the following:
Choose Window > Open Step Editor.
Drag the Step Editor button, which changes to the Step Editor window as you drag it.