In Android 12 on my Galaxy S10+, without PC, how to use "toybox"

I know that Android internally uses Toybox as its basics for Linux sh commands. And in Internet I can read about toybox the help doc. == Presumably since I do not want to have connection to a computer, there is no possibility in Samsung Galaxy S10+, Android 12, to use ADB. Am I right? == Thus, in my smartphone by itself, how can I invoke toybox and use toybox its shell commands. This, please, as a general question. == Now especially, this I want to do while programming a Button in Total Commander. E.g. as a first test, I wrote in the Button "toybox --version". This works. == Then ongoing I want how to use the sh copy command "cp" (exhausting all options). == Then how to use shell variables. In toybox there seems not to exist Parameter Expansion with "$variablename". How is the usage of variables in toybox, thus in Android? I mean general shell variables, beside the parameters defined for the Buttons, e.g. %P, %T, %M, %N, ... == In Internet there is no article about these items. If needfull, I am willing to learn Java, and have already bought a thick book. Is there a intraductory documentation regarding these itens. == For other purposes I use Termux. But Termux has no direct access to the files and variables as I need in in Total Commander Buttons. Thanks, Regards