I intend to generate this sketch using tikz, but was unable to do so. I was trying to fiddle with the following code:
\documentclass{article}
\usepackage{amsmath,mathtools}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}
A \arrow[rd] \arrow[r, "\phi"] & B \\
& C
\end{tikzcd}
\end{document}
I need some help here. Also a good reference for tikz would be appreciated, specifically, I am not able to understand the function of "&" in tikz environment.