Click on the calendar button in Outlook

Click on New Meeting button

Type in the name of your meeting in the "Subject" field

Click on the "Rooms..." button

Double click on the room(s) that you may want to use.  You will see the available time slots for each room in the next step.  Click OK.

Click on Scheduling assistant

Click on the left side to add attendees.  Find an available time slot on the right. 

Check the box of the conference room you would like to reserve

If you're happy with the time and location, click send.

If there are no conflicts, the conference room will automatically accept your request, and all attendees will receive a meeting invite.