it's called "system programming"....in this kind of questions u have first of all to plan what Classes u want to define, and what fields/methods do each class have....for example I can see that u need to define a Class named "Subscriber"
which have the fields=(first name, last name, tele number etc...)
be attention that u make a Class name TelephoneDic for example and implement the supplied methods(print delete etc..) telephoneDic Class may contain a List of Subscribers....or any other data stracture(it depends on question)
i took this course in c/c++ a year ago...idk if c# got that difference but the concept is the same .