cmd-W closes windows and cmd-Q quits the App. That Apps can stay open without having a Window is actually useful (at least it makes sense to me).

@screenshot

Mac has always been kind of amazing for the granular options you get to take screenshots out of the box.

• Command - Shift - 3 | Takes a fullscreen pic of the entire display. Loads a preview in the bottom right corner. Click to expand, and from there edit, share, save, delete, etc.

• Command - Shift - 4 | Turns your mouse cursor into a crosshair. Drag to create a rectangular window. Takes a capture of the contents when done. Escape or right-click to cancel. Preview loads the same as above.

• Command - Shift - 5 | Brings up a rectangular section that can be moved around and resized.

But any shortcut can be remapped:

Go to System Settings > Keyboard > Keyboard Shortcuts > Screenshots