I have the following cube(taken from there):
\documentclass[border=5pt, multi, tikz]{standalone}
\usetikzlibrary{quotes,arrows.meta}
\begin{document}
\begin{tikzpicture}[every edge quotes/.append style={auto, text=blue}]
\pgfmathsetmacro{\cubex}{6}
\pgfmathsetmacro{\cubey}{6}
\pgfmathsetmacro{\cubez}{6}
\draw [draw=black, every edge/.append style={draw=black, densely dashed, opacity=.5}, fill=white]
(0,0,0) coordinate (o) -- ++(-\cubex,0,0) coordinate (a) -- ++(0,-\cubey,0) coordinate (b) edge coordinate [pos=1] (g) ++(0,0,-\cubez) -- ++(\cubex,0,0) coordinate (c) -- cycle
(o) -- ++(0,0,-\cubez) coordinate (d) -- ++(0,-\cubey,0) coordinate (e) edge (g) -- (c) -- cycle
(o) -- (a) -- ++(0,0,-\cubez) coordinate (f) edge (g) -- (d) -- cycle;
\path [every edge/.append style={draw=black, |-|}]
(b) +(0,-5pt) coordinate (b1) edge ["6"'] (b1 -| c)
(b) +(-5pt,0) coordinate (b2) edge ["6"] (b2 |- a)
(c) +(3.5pt,-3.5pt) coordinate (c2) edge ["6"'] ([xshift=3.5pt,yshift=-3.5pt]e);
\end{tikzpicture}
\end{document}
I would like to write and draw things in that cube, like this:

How I can do this?

