Arranging Additional Screens
To arrange a second screen:
Settings > Displays > Arrange...
Move your mouse between where the two screens join.
If the mouse ends up crossing too high on Monitor 2, drag Monitor 2 down slightly until the cross-over lines up.
To rotate your monitor's screen, scroll right down to the very last option in the Display menu, and select what level of rotation you require (90°, 180°, 270°).