a MWE of LaTeX3 package

How do I write a XeTeX program from this package which just prints the result of this command

use_i_ii:nnn { abc } { { def } } { ghi }

when called as a function $foo{ abc } { { def } } { ghi }$
to an output page like this:

$abc{def}$

What I need is a MWE with all the stuff around:

documentclass{article}
ExplSyntaxOn
cs_new_protected:Npn

…
I’m currently unable to create a MWE. IN particular, I’m unable to guess this line:

cs_new_protected:Npn

with variations of protected:Npn

YOUR COMMENT GIVES THIS ERROR YET AFTER UPGRADING MIKTEX:

    Command Line:   D:ProgramFilesMikTexNEWmiktexbinx64xelatex.exe --interaction=errorstopmode --synctex=-1 "ideje31.tex"
Startup Folder: C:Usershynek0DesktopTH0dipl

This is XeTeX, Version 3.14159265-2.6-0.999991 (MiKTeX 2.9.7050 64-bit)
entering extended mode
(ideje31.tex
LaTeX2e <2018-12-01>
(D:ProgramFilesMikTexNEW2tex/latexbasearticle.cls
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class
(D:ProgramFilesMikTexNEW2tex/latexbasesize10.clo))
! Undefined control sequence.
<recently read> ExplSyntaxOn 
                              
l.3 ExplSyntaxOn
                   cs_new_protected:Npn
? 

! Emergency stop.
<recently read> ExplSyntaxOn 
                              
l.3 ExplSyntaxOn
                   cs_new_protected:Npn
No pages of output.

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 PDFLaTeX Compilation Report (Pages: 0)

 Errors: 2   Warnings: 0   Bad Boxes: 0
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