Open your Outlook calendar. From your calendar, look for the little arrow on the Open Calendar button (top bar), and choose From Room List from the drop-down menu.
Type Library to find the calendars for the 3 library rooms. Double-click the room you are interested in. The room name will appear at the bottom of the box. Click OK to see the room's calendar. Check the dates and times to see when it is available. You can repeat this for any rooms you want to check.