I need more explanation for special areas in OSPF routing protocols?

ospf area type normal area ,backbone area,stub area,total stub,nssa area all area connected  to area 0 means backbone area because backbone area pass out the route and stub area external routes not allowed in stub area and total stub area external routes are not allowed in totally stub area but the routers in the totally stub area can connect to the extranal router via the defalut router that is injected in the ABR and Nssa area the ASBR of an NSSA can import external route informatin in the area...