In order to get yourself able to build complex object oriented programs,i suggest you first start with simple programs...
Try this:
Create a family,that has one father,one mother and two children.Father,mother and children are all humans,so they inherit from a class human.Every human has a name ,a surname and an age.Every father has a job and his favorite sport.Every mother has as well a job and shop for clothes.Every children has as its attribute the school he is going to and his best friend.All attributes described(e.g. age of human) are data members of the respective class.
After constructing your classes,just go and create the family i just described in your main.Feel free to add some attributes if needed,give preferred names ,or even create your own family(it might has more than two children).
Again,when you find yourself in doubt about the requirements,take arbitrary decisions ,which of course make sense in terms of OOP (object-oriented programming).
I think that is a good very first step :-)
Hope this helps