If you're working on more than one document or spreadsheet at the same time, it can help to see them side-by-side.
See windows side by side in Windows 10
Drag one of the windows to the edge of your screen.
Select the app you want to see next to it.
See two documents side by side in Word
Open the 2 documents.
Select View > View Side by Side.
If you scroll up or down, the other scrolls as well. If you want them to scroll separately, select Synchronous Scrolling to turn it off.
Split your window into panes in Word and Excel
Select View > Split.
To resize the panes, just drag the border.