If your monitors are the same make and model, you can probably skip this section—once you plug them both in, Windows should automatically extend your desktop horizontally. Just adjust each monitor’s stand so they line up perfectly, and you’re off to the races.
If you have two different monitors, however, you may need to do a bit more work to make them play nicely with each other. For example, maybe you’re plugging your laptop into an external display and using them side-by-side, or maybe you have one 4K monitor next to a 1080p monitor. This will produce some weird behaviors, but they’re easy to fix: just right-click the desktop and choose Display Settings.
Under Select and rearrange displays, you can click and drag the rectangles around so they match the monitors’ orientation on your desktop—say, if one is slightly lower than the other. That way, when you move your cursor to the left, it’ll appear in the same spot on the left monitor, rather than jump up or down on the screen. You may have to do a little trial and error to get them lined up properly.
Scroll down to the Scale and layout section, and you can adjust the resolution of each monitor and its scaling. So, if one monitor is 4K and the other is 1080p, you can set each monitor to its native resolution but increase the scaling on the higher-resolution one, so your windows appear the same size on each. (If you want to set up a monitor in portrait mode, you can do that here too).
If you want to go even further, you can use each monitors’ built-in settings to adjust brightness and color to make them match as closely as possible. (An app like ScreenBright can make this a little easier, if your monitor supports software controls). Once you’re done tweaking all these settings, your monitors should match up much more closely, making it easier and more pleasant to move windows between them.