The release manager for a given month is the person in charge of lining up speakers, sponsors, food, and beverages for that month. They'll also be the MC at the meetup itself. Responsibilities at the meetup mostly involve making sure things get done on time.
Often, there's a stable of speakers and sponsors. So, even if you don't know anyone who wants to speak, you shouldn't hesitate to sign up and just ask other release managers if anything's already done.
Travis Swicegood and Jeremy Boyd are in charge of maintaining relationships with sponsors, so get in touch with them.
6:30: Food, beverages, mingling
7:00: Meeting called to order. Group announcements. Time allotted to sponsor.
7:10: First talk
8:00: Second talk
8:45: Lightning talks (2-3)
2014 Release Manager Signups