Rooms and resources are not directly reserved on their Google Calendars. Instead, they are added in the same area where people are invited to calendar events. Check the resource calendar to make sure there is no conflict and then you can reserve the room or resource.
To do this, create or edit an existing event on your Google Calendar. You can double click an existing event or double click in an open space to get the the full event editor window.
After you add title, date, and time information, select the Rooms tab
Once you have selected your room/resource, your reservation should show up as an event in your calendar and then a few moments later show up in the room/resource's calendar as well. If you move your event or cancel it, these changes will be reflected in the other calendar, as well.