By default, the 'View Side by Side' option shows two spreadsheet windows horizontally (one window is on top, one is under).
To change the view, click on 'Arrange All' in the 'Window' section of the 'View' tab .
The 'Arrange Windows' dialog box appears. There are options:
'Vertical': 2 windows will be placed side by side, just like when you align them to the left and right of the screen (as above).
'Horizontal': 2 spreadsheet windows are placed horizontally (one window is on top, one is under).
'Tiled': In case you open 2 spreadsheets, 'Tiled' will act like 'Vertical', placing 2 spreadsheets on the left and right sides of the screen.
In case you open more than 2 spreadsheets, 'Tiled' will arrange them into cells on the screen, depending on the number of windows opened. Same as the picture below:
'Cascade': Spreadsheet windows are arranged in hierarchical form.
If you want to scroll to view two (or all) spreadsheets at once, you can turn on the 'Synchronous Scrolling' option in the 'Window' section of the 'View' tab. At that point, you can scroll through both spreadsheets when moving the scroll bar on a window. This approach is useful when you want to compare two spreadsheets to find differences.