Although recording MIDI on an existing track is a common way to create new MIDI regions, it is often desirable create new MIDI regions as part of the editing and/or arranging process.
A new MIDI region can be created with the mouse by entering Draw Mode (entered by pressing the d key or clicking on the Draw tool) and then left-clicking anywhere in an existing MIDI track; this will create a region that is one bar long. If longer regions are desired, they can be created by left-clicking anywhere in an existing MIDI track and dragging the mouse until the region is the desired length.
Once created, all the typical methods of editing audio regions will work the same as they do for MIDI regions. See Editing Regions and Selections for more details.