You can click on the yellow ball upper left of the window, the minimize icon, to minimize the window to the dock.
The minimized windows appear in the right side of the dock.
The right white sheets are the minimized windows.
The macOS dock paradigm is a little different than windows. The mini-small black triangle below the app icon indicates that the app is running. You can see that I have terminal, system report and acrobat reader running. I have my dock icons to expand when the mouse pointer is over an icon. I have a minimized folder and three three application windows minimized.
This would seem about the same as windows, I think.
Robert