When I post a reply to a thread, what does this mean?:

You could set up the board so that each post has to be reviewed by a moderator before it’s publicly shown. Needless to say, we don’t have time to review each post at the SDMB so the message doesn’t really apply.
The poll stuff probably means that there’s a further step involved when you create a poll (a feature currently disabled at this board.) I’ve never done it but I’m sure some of our posters have at other vBulletin boards that enable the feature and they can probably explain it.