Al and all of the alcohol dehydrogenases do one thing: they snip off a specific pair of hydrogen atoms from an alcohol and stick one onto a molecule called NAD. (The other hydrogen atom is simply let go and it floats away.) This change turns the alcohol into an aldehyde (acetaldehyde in the case of ethyl alcohol). This is the first step in the pathway for detoxifying alcohols in the human body. All workers carry out similarly tiny steps; it's only the sum of many them put together that make up the traits we can see in a living thing.

In the picture, all of the hydrogen atoms are shown in white. The remaining kinds of atoms are colored based on the molecule they're part of: brick red for ethyl alcohol and acetaldehyde and aqua for NAD.

NAD is a molecular storage bin for hydrogen atoms. Many kinds of worker paste hydrogen atoms on it, and many others use it as a source of hydrogen atoms.