A few quick answers —
>Why do folders all open in a new window?
Spacial Finder (see https://arstechnica.com/gadgets/2003/04/finder/). It remembers window position, icon positions within the window, and the like.
>Why can't I maximize a window by double-clicking the title bar? Why can I only resize windows with the little handle in the bottom corner?
Nobody really thought about maximizing by double-clicking, as there was the maximize button available, that maximized not to the screen but to the content being presented (at least that was the intent). Double-clicking on the title bar made the contents of the window disappear while keeping the title bar hovering there. This was great on small screens so that you didn't have to click between windows that had information in them but could hide the top one, read the one below, and go back to the top one without moving the mouse.
As for the little handle, that was for a) the sake of consistency, and b) because that was the one way the OS did things; resizing windows worked just that way. Not sure if that was purely intent or if it was due to system resources, especially in earlier Systems.
>What is the point of the settings dock in the bottom left of the screen? Do I really need to change resolution and colors that often?
I remember using settings much, much more than on current machines — there were a lot of little tweaks one might want to make for performance or ease (changing colors or resolution might be necessary due to a game, for instance, whether for speed or compatibility if it were older).
>Why do I have to browse the whole hard drive to find any of my applications? Why can't I right-click files/folders?
That was simply the way of things, though there were plenty of extensions out there that put application links (or links to pretty much anything) into the Apple menu, which became a catch-all that Apple has pared down (in response?) to almost nothing.
>What is the point of the bigger/smaller window button, why not maximize? Why does minimizing just collapse windows to their title bar?
See above.
>How do you even turn off the computer?
Choose shut down, and turn it off with the switch when it told you it was safe to do so.