You can use Snap to arrange windows side by side, which can be especially helpful when comparing two documents or when moving files from one place to another.
(Snap might not work on some programs that have custom window behaviors.)
Drag the title bar of a window to the left or right side of the screen until an outline of the expanded window appears.
Release the mouse to expand the window.
Repeat steps 1 and 2 with another window to arrange the windows side by side.
To return the window to its original size, drag the title bar away from the top of the desktop and then release.