This notation is called cross-staff notes.

You can search for info about cross-staff notes in the on-line manual.

Basically you first enter all the notes in one staff.

The layout will - temporarily - look awful because of all those ledger lines.

 The smartest/fastest way to the cross staff layout is via the Cross Staff plug-in (located in TG Tools).

There is even a handy keyboard shortcut:

Drag-select the note/region you need to move to the other staff.

Then hold down the correct modifier key *) - and hit the UpArrow key or the DownArrow key to move the selected to the staff above or below.

*) Are you using Windows Finale or Mac Finale?

mac finale