What you have there is a class definition. That in itself doesn't do much - you need the class code to go with it.
With classes you first have to create an object from the class. The creator of the class may have done this already for you, or you may already have done that. Classes are a complex subject.
You create a class object kind of like making any variable type:
alarm_clock myAlarm;
Then you can access any of the functions within that class by referencing them as methods of the object:
byte triggeredAlarm;
triggeredAlarm = myAlarm.run();
triggeredAlarm will then contain the results of the run() function from inside the myAlarm alarm_clock object.