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Yours is a question that's best addressed in full length books about OSPF design. Basically, you only really need multiple OSPF areas for scalability. There are many factors that impact OSPF scalability. There was an old rule-of-thumb of no more than 50 routers within a single OSPF area, but today you might have hundreds of OSPF routers with the same area while conversely, also even today, 50 may be too many.
If you do need OSPF areas, then you need a backbone area, area 0, and there are different types of non-backbone areas, and different options for how they interact and interconnect. Again, many variables, also generally dealt with full length book about OSPF design.
Cisco has a condensed OSPF design guide: http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml
