I can explain the Mac bits. The command key (⌘) is the primary key and is used to implement system-wide (via convention) shortcuts: e.g. copy, paste, find, min

I can explain the Mac bits. The command key (⌘) is the primary key and is used to implement system-wide (via convention) shortcuts: e.g. copy, paste, find, minimize window, etc. The option key (⌥) is used for symbols and composing diacritics. The ctrl (^) key is a tertiary key, used for a small amount of keyboard navigation. The fn (globe) key is largely unavailable for use in shortcuts. There is no apple key, it got replaced by the command key. Since the command key does a lot of work, you end up with a lot of chording.