TidBITS:

The Dock has been a core aspect of the Mac experience since the earliest days of Mac OS X. In fact, the Dock actually predates Mac OS X, since it was also prominent in NextSTEP. It displays open applications, offers a quick way to launch favorite apps, and holds shortcuts for documents and folders.

You’ve probably used the Dock so often and for so long that you don’t think about it. I’ll explain everything the Dock does, from the basics to tweaky capabilities that may be new to you.

The Dock is easy to take for granted, but it’s a key part of your everyday Mac experience. Mastering its nuances will help you work faster, more comfortably, and more efficiently.

The macOS Dock seems pretty simple but there’s a lot of under the hood power in it. This is a good description of all the things you can do with it.