Understanding macOS's Keyboard Shortcuts

"Move focus to active or next window". If I have multiple windows running, what's the "active" or "next" one?

This will put the focus on the topmost window of the currently active application ( which itself can be toggled by super+tab / Command+Tab ). This allows you to input keyboard commands to that window even if it somehow lost focus.

If the topmost window already has focus, it will rotate to the next-topmost window, regardless of which application it belongs to. This might cycle through a mixed set of Finder windows and Chrome windows based on this 'z-index'. This is the order they visually appear in, such as which was most recently clicked or opened.

"Move focus to the window toolbar". What's the window toolbar?

This is a kind of control that some OS X native applications use. In Finder you can see it is used to select the kind of file view to display (icons/list/etc). Not many applications seem to have bothered with this.

"Move focus to the floating window". What is the floating window?

This is a kind of special window that some OS X native applications use. It remains on top. Not many applications seem to have bothered with this.

"Move focus to next window". What's the next window? And how does this shortcut differs from the first one in this list?

This will move the focus to the next window of the currently active application. Switching between multiple Chrome windows, for instance. It will not, unlike the "Move focus to active or next window" function, select windows belonging to a different application.

"Move focus to the window drawer". What's the window drawer?

This is a kind of control that certain OS X native applications have in their interface. Not many applications seem to have bothered with this.

"Move focus to status menus". What are the status menus?

The status menus are the items in the top right corner on default settings. This include the clock and your username (the logout/shutdown menu), as well as any icons added by applications.

They really could have been named better, or have tooltips, but a lot of the descriptions would likely be oxymoronic as they aren't easy to explain in a vacuum. Some of the issues appear to be the legacy features in OS X that were intended for use by app developers that didn't become very well known or popular.

Corrections or additional examples are are welcomed in the comments.

The easiest way to see the behavior is to try the shortcuts. For example, the window toolbar is the top part of the Windows (where the find field is, and possibly other buttons). The floating window might or might not be there, but the help window is a floating window, among others.

Open a few windows and test. Most of them will start to make sense.