We are the lowly scum of the earth that specifically single out members to harrass on a daily basis.
Ofcourse, I am kidding.
A moderator is an individual who basically helps to maintain the forums. We make sure all the forum rules are being followed and help to get rid of troublesome posters, spam, etc....
We also are here to help answer any questions about the site and provide info regarding how many of the site' s functions work.
In terms of being selected as a moderator, I cannot speak for the others. But, my understanding is that, periodically, administration asks the current moderators for suggestions for one or two new moderators to be brought on board. The current moderators discuss some members that fit the moderator " mold" based on their past posts and actions on the forums. Then everyone basically votes and administration contacts the member to see if they are interested.
In your case, if you have an interest, I would suggest contacting administration through the link above and asking them this very question. They may have a better answer for you.