Many new BBQers post questions on rib cooking methods, one of the most common is "How do I tell when ribs are done?"
Perhaps the most used method is the bend test. Simply pick up the rack of ribs from one end with tongs, with the end of the tongs at about the 5th or 6th rib in(slightly less than 1/2 way). If the ribs bend at a 45° angle or more they are done.
Ribs done like this will not be "fall of the bone", if that is your preference keep on cooking past this point until they reach that stage.