Linux (and Mac OSx) being based on Unix follow the Unix philosophy of having small, single purpose tools.
Small, single purpose tools that "do one thing and do it well" that can be combined by the user to achieve whatever they want done.
Now that you own a Kindle, you also own a working version of (embedded) Linux. Like it or not, you got it.
Unlike some widely distributed operating systems, which have a choice of one (1, 1!) gui user interface, *nix systems have many choices in gui interfaces.
And can even use multiple ones, on the same machine, at the same time.
This situation of not knowing what gui interface a reader using a *nix system might face (pun intended), the common practice is to give directions in terms of the command line tools.
(Many, say most, of the command line tools are "standardized".)
So as an aid to people who have never or only rarely ventured outside of the world of "click this button" - - -
A decent crib-sheet of the 687 commands you are likely to want information about in your *nix reading:
http://onlamp.com/linux/cmd/