
If you already have a window open in fullscreen, you can easily place it side by side with another window by opening Mission Control:

Split-screen is the ability to easily view two applications side by side on a single monitor. So, buckle up, you’re about to learn how to organize your digital life to maximize your productivity and minimize your frustration. The goal of this article is to help you take your Mac desktop organization skills to the next level using a mix of native Mac features, such as Mac Split Screen, and third-party windows management applications. But as convenient as the ability to minimize, maximize, move, and resize windows is, it can still sometimes be difficult to maintain a neatly organized desktop where every application has its place.

Most Mac users wouldn’t be able to imagine what it would be like to be limited to a single open application window at a time.
