Root Servers and Forwaders ?

[Rahul Parasnis]

Hello 
I am asking a very basic question Here? 
In the Example described on Page 28 DNS and BIND 3rd Edition 

Resolver query for giri.gbrmpa.goc.au 
The query first goes to  "." then to "au." then "gov.au" and then to
"gbrmpa.gov.au".

First Question : How does that First query goes to "." ?  
What if I have specified "Forwarders" in my named.conf file ? 

How does the query work , if it is given from the host 
     piripiri.finance.gen.au   where gen.au and gov.au are same level zones

Second Question : What should  gbrmpa.gov.au or gov.au server have in the
db.cache file ?
Should these servers also have the file downloaded from ftp.rs.internic.net ?
How does these root Serers work for the subdomains like gbrmpa.gov.au ?

Simmilarly on Page 31 , 

1.Nameserver A receives query from the resolver 
2. A queries B ( How this works ? Which line in the Named.conf does this?
does "forwarders" is doing this function ? ) 

I am really confused about the concepts of "forwarders" and "root Server"
functions.
How does they work for subdomains like  finance.gen.au and gbrmpa.gov.au ?

Thanks a lot for any clarifications !! 
- Rahul