Multiple Staves
When you have parts on several tracks selected in the Project window, these are put on one staff each when you open the Score Editor. This allows you to work on several staves in parallel.
The settings in the Score Settings dialog (Staff tab) are specific to each staff. You can keep the Score Settings dialog open and select one staff after the other, make your settings, and click Apply.
If several staves share settings, consider saving a staff preset, and apply it to the other staves one at a time.
You can select notes from one or several staves at the same time, using any of the selection methods.
When you enter or edit notes, use the Mouse Value display on the status line to determine the pitch. Whether a note ends up on the upper or lower staff is governed by the Split Point setting in the Score Settings dialog (Staff–Polyphonic tab).
If you want to put two notes with the same pitch on different staves in different parts of the score, use polyphonic voicing.