I am not sure if my following example is good for creating equations with notes of current mathematical operations:
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\begin{document}
\begin{align*}
x \cdot 5 &= 5 && \lvert \; \div 5 \\
x &= 1
\end{align*}
\end{document}
Is this the correct way to define these type of equations? Is there any other package which does the same in a better way? How would you create this equation?
align*
is already an outer mathmode environment, you should remove\[ .. \]
.