1. With note input enabled, press Shift along with the up/down arrow keys to extend the caret onto adjacent staves.
  2. Now, when you enter notes, they will be created on all staves the caret crosses.
  3. Input other notations, such as slurs and articulations, dynamics etc. and they will be created for all staves.
  4. When using a MIDI keyboard, as you play chords Dorico will automatically explode them across the staves.