I'm thinking of doing some spin classes at my gym at work, but I have no idea what to expect.

I've gone in there when there isn't a class and tried out the bike, so I know enough to not expect it to feel like riding my bike outside.

What are the classes like? Why don't the bikes have a cadence monitor? Do I need to bring in my HRM?

I just don't want to be the idiot who has no clue the first time I go to a class

Thanks,
Kate