1. Navigate over to https://outlook.office.com/ and sign in if required.

2. Click on the Calendar icon to open your Calendar:

3. Pick a date for the meeting and double click on its tile on the right hand side.
4. Fill out the details as appropriate and be sure to invite the Meeting Room itself as one of the attendees:


5. Once you click the Send button, the staff at the reception desk will receive a notification that will let them either Approve or Decline the meeting.
If approved, the meeting will appear in your own calendar after a few minutes.  If the meeting room does not have someone delegated to accept/decline meetings, it will automatically accept them.