Go to your Outlook calendar and select "New Meeting"

Fill in your details like normal when setting up a meeting, where it says location there should be a room finder tab at the end.

Once clicked on the room finder, you can filter what building, what floor or all meeting rooms you would like to see and depending on what time you would like the meeting booked for, it will display what meeting room is available at that time

Choose the available meeting room that suits you, then wait for your meeting to be accepted by the room.  

After it has been accepted, you should see it in the meeting room calendar.