Hover over the event to see what space is already reserved. This will help you determine where there is open space available for rent.
The Banquet Room consists of Civic A plus Civic B plus the Training Room. If you are looking for any of these rooms and you see that there is an event in the Banquet Room, that means that Civic A, B and the Training Room are all booked.
Likewise, if you are looking for the Banquet Room and see that Civic A, B, or the Training Room have events, then that means the Banquet Room is unavailable.