I've gone to a couple of these in the past, and usually there is no charge, and no tickets to reserve. You just show up (well in advance for this one, probably). Once time is announced, you can plan appropriately. Since these are during daytime, workday hours, many who might like to attend are not able to, so usually seating is available for everyone who shows up. I'm planning to go to this one - Jerry Herman has always been one of all all-time favorite composers, and one of the rare ones who beautifully wrote both music and lyrics...