Open the Piano Roll editor
Select the MIDI notes you want to edit
Click the Pointer tool
Drag a note left or right to change its start position
Drag a note up or down to change its pitch
Drag the right edge of a note to change its length
Drag the left edge of a note to move its start point and length
Use the Velocity lane to change note velocity
Use the Quantize settings to align notes to the grid
Use the Region Inspector to adjust note timing and other MIDI parameters
Use the Event List for precise note-by-note editing
Press Command plus A to select all notes in the region
Press Shift while dragging to constrain movement
Use the Pencil tool to draw new notes
Use the Eraser tool to delete notes
Use the Split tool to cut notes
Use the Mute tool to mute notes
Use the MIDI Transform window for batch note editing