[latex] Adding a caption to an equation in LaTeX

The \caption command is restricted to floats: you will need to place the equation in a figure or table environment (or a new kind of floating environment). For example:

\begin{figure}
\[ E = m c^2 \]
\caption{A famous equation}
\end{figure}

The point of floats is that you let LaTeX determine their placement. If you want to equation to appear in a fixed position, don't use a float. The \captionof command of the caption package can be used to place a caption outside of a floating environment. It is used like this:

\[ E = m c^2 \]
\captionof{figure}{A famous equation}

This will also produce an entry for the \listoffigures, if your document has one.

To align parts of an equation, take a look at the eqnarray environment, or some of the environments of the amsmath package: align, gather, multiline,...