When you say "big people" do you mean famous people,or adults? If we are talking about famous people then usually everyone knows who we mean,and in the West there are not so many people with the same family name.If there are then we add the first name or the title,for example "George W Bush" because his father was also called George Bush. Or we say "Junior" to show we are talking about someone's son.

It applies to all people: call them by their first name, or call them by their surname. In general, first names are used in informal situations, and surnames in more formal ones. But this is a generalisation! Example: Fred Smith might be called Fred by his friends and boss. But his boss might call him Smith. Fred's boss might call him Fred when he is feeling friendly, and change to Smith if he is not happy with Fred. Using surnames with Mr/Mrs/Miss/Ms is more respectful than using surnames on their own. Military officers call ordinary soldiers by their surname or rank, or rank plus surname. Using a first name would not be appropriate. Teachers often used to call boys by their surname only - making it clear that the teacher was 'superior.' Girls used to be called by their first names, usually. Nowadays both girls and boys are called by their first names, usually. Rich people could address their servants by their first name or surname, but servants could only address their employers by their title plus surname. The rules of society are complex. Using or not using titles, using first names or surnames, can suggest all sorts of things about the relationship. About celebrities: Brad and Angelina are known by their first names, not as Pitt and Jolie. However, Jason Statham gets called Statham, not Jason. Who's in that film? Oh it's Statham, Stallone (not Sylvester!) and Craig (not Daniel). Who's the star of Terminator? Arnold or Schwarzenegger? Not Arnold, but Schwarzenegger!