Open Multiple Windows Side-by-Side

Drag a tab or window to an outer corner or side of your screen. When it snaps to the location you want, select another open window to place beside it. They will line up nicely without manual adjustment. You can then adjust the relative size of the windows by dragging the gray bar between them.

Instead of dragging, you can also use keyboard shortcuts: WINDOWS + arrow (left, right, up, down) to snap the windows into place.