In your Outlook Calendar, select the day you wish to schedule a meeting. Right-click on that day and select New Meeting Request. You can also click on New Meeting located on the Home tab.
Enter the meeting participants in the To… field. Click on Rooms… to the right of Location to select the room you wish to book.
Double-click on the desired room and click OK.
You should see all the participants and the room number in the To field. The room number is also listed in the Location field.
If the room is available, you will get a confirmation that the meeting request has been accepted and the calendar will be updated accordingly.
If the room is not available, you will receive a notification that your request was declined. At that point you will have to go back to your original in your Outlook Calendar and update the day/time/room and re-send.