Windows 10 Snap (or Snap Assist) allows you to easily arrange multiple open windows on your screen
To snap two window side by side
1)Click the title bar of an open window and drag it to the left or right side of the screen
2)As the mouse pointer touches the edge of the screen you will see a visual indication that it is ready to snap (as per image below)

3)Let go of the mouse button and the chosen window will snap to the edge of the screen
4)Snap Assist will then show all other open windows as thumbnails (as image below) and you can click on one to make it automatically snap to the edge of the screen, beside the window you snapped above

5)Both windows will now appear side by side (as per image below)

6)You can widen or narrow each window by clicking the dividing line between the windows and dragging to the left or right (as shown below)


To snap three or four windows
Follow same steps as above, but drag to the corner of the screen rather than the edge of the screen

Snapping windows using keyboard rather than mouse
You can also snap windows using the keyboard
To do this make sure chosen window is active and then press Windows Key and Left or Right arrow to snap it to chosen side
+
/