Think about what kinds of things and processes you want to model in your program. Determine what information is needed for each object. For a person, that might include name, date of birth, address, etc. or it might not. You have to deside what information is important for each of the objects in your situation. Then decide what each object should be able to do; this will be used to create member functions. Some member functions will control how your data is stored (validation) or retrieved (formatting). Some member functions will cause the object to interact with other objects or change its own states. You have to determine what each type of object should do.