Just as in the vast majority of other European countries the majority of Serbian surnames are patronymic. This means that the surname Jovanovic would be derived from one of the ancestors with the name of Jovan. In some very rare cases you can see the metronymic naming, but this is very rare.
The way surnames originated can be diplayed on the following way:
Patronymic; naming after one of the ancestors,
Occupational; naming after ones profession e.g. Strugar,
Geographical; being named after a geographic location,
Descriptive; being named after a special physical feature inside ones family,
Anecdotal; being named after a particular event in ones live,
The majority of surnames in Serbia end with –vić. However in 9-10 cases most people with the same surnames are not related at all. Names like Jovanović, Petrović, Djordjević, Pavlović etc. are comon surnames all from Patronymic naming. Since names like Jovan, Djordje, Petar and Pavle are comon surnames in Serbia its more then normal to see Patronyms of these names.
The confusion factor
So if my surname is e.g. Djordjević or Jovanović then my ancestors were Serbian? Not exactly, patronyms named you after your ancestor. And Although in many cases the above would be true it does not give you a garantuee. For example, there are many Roma families with the above surnames. They might have Serbian surnames, but they are not.
The geographic distribution of a surname is also confusing. The surname Petrović is being used inside Serbia and Croatia. Actually, in Croatia they use the same similar naming system as in Serbia. There are however surnames that are typically Serbian, but a 100% garantuee you never have until you research.