With a pair of monitors hooked up to a graphics card with at least two outputs you have all sorts of options. Windows has always supported dual monitors but since Windows 7 support has been very good and with Windows 10 it's pretty seamless.
For best results you need a pair of monitors running the same screen resolution, ideally a matched pair, so that as you move the mouse between them there's no jump. But you can of course use whatever you have to hand and it'll still work.
It means you can run an app or game on Screen 1 while you have a browser, film, TV or other apps running on Screen 2.
Personally I prefer dual monitors over a single large monitor. Yes a large 1440p or 4k monitor gives you lots of screen real estate, but there still a strong case for having an additional monitor. As a designer I like to have my main app maximized on my primary monitor and then I have reference material open on my secondary monitor. Obviously this is possible on a large single monitor too, but would mean messing around with window resizing.