I know that $X \iff Y$ is true when
$X$ is True and $Y$ is True
$X$ is False and $Y$ is False
I know that there is a simple algorithm to convert to CNF form, but I don't remember it...
$$(x \leftrightarrow y) \Leftrightarrow (x \rightarrow y) \land (y \rightarrow x) \Leftrightarrow (\lnot x \lor y) \land (\lnot y \lor x) $$