Latex: How to encapsulate text in an amsmath block

Question

My first stackoverflow question. I take the easy way out and directly ask the following. How is it possible to produce an output in LaTeX, like the one pictured below?

More holistic, what are the best ways to encapsulate text in an amsmath eg. equation, align, block?

Answer 1

You can use the \text{} command to write text in amsmath blocks:

\documentclass[11pt]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
    ID_V &= \text{identifier of $V$} \\
    P_C  &= \text{password of user on $C$}
\end{align}

\begin{alignat}{2}
    &ID_V &&= \text{identifier of $V$} \\
    &P_C  &&= \text{password of user on $C$}
\end{alignat}
\end{document}

Answer 2

You should use a tabular environment. This code:

\documentclass{article}

\begin{document}

\begin{tabular}{ll}
$ID_V$ & = identifier of $V$\\
$P_C$ & = password of user on $C$\\
$AD_C$ & = network address of $C$\\
$K_V$ & = secret encryption key shared by $AS$ and $V$
\end{tabular}

\end{document}

produces:

Then you can indent or align the tabular as you prefer.

Only a hint about the second part of your question. Keep in mind which environments, like tabular, have text as default content (hence math must be included in $...$) and which ones, like array, align, equation, etc., have math as default (so that text must be included in a box or in \text{...}).