You can book a room using Manhattan. We have a desktop version and a mobile version you can access on your mobile phone.
click the Add button
Fill in the date, time and how many attendees there will be and if you're lucky a room will show up. From there click Book
It's good to book a meeting room a day or two early in order to get a room. They fill up fast.
You'll also have to show up 15min before the meeting starts to confirm you're there or the room will be bumped and someone will swoop in and steal it from you. A lesson you only have to learn once.