The modules like po, ap,ar are come under operating level
this modules are also called multiorgmodules because this
modules table have column ord_id and have multiple 
organization information.
  _all is last we can identify is multiorgtable 

PO and AP are done below the SoB level in a MOrg environment.

HR - Business Group level
GL, FA - Legal Entity Level
AP, AR, Purchasing - Operating Unit Level
Inventory - Inventory Unit Level

Payables and Purchasing are known as Sub-ledgers.Sub-ledgers
data is secured/separated by operating units. Hence PO & AP
are implemented at Operating unit level.

Manual payment is used to pay the invoices manually using
out checks,whereas quick payments are made thru EDI/EFT or
inside clearing or bank transfers in a batch.

In a manual payment every time we have to go on payment 
side and approve the payment for every transcation. its 
like an check

Quick payment

Edi electronic data interface can use to pay the amount

Balnce : Only balncing segment will be copy by Dr. side & 
rest will be copy by Financial option.

Account: only account will be copy by Financial option & 
rest will be copy by Dr. Side

Automatic offset method:
If you enter invoices for expenses or Asset purchases for 
more than one balancing segment, you might want to use 
aotomatic offset method to keep your payables transactions 
accounting entries balances.
Balance : The liabilty account for balancing segment value  
take from invoice distribution & rest segment values will 
take from invoice header
Account: The libility account for account segment value 
takem from invoce header & rest segment values will take 
from invoice distribution.
None : The liability account for all segment values take 
from invoice header.

1)If you enable "Balance": It will replace the Balancing 
Segment level only while generating an accounting entry for 
distributing the invoice. For example, you have raised an 
invoice to purchase stationary for company two (02)and your 
default liability account is 01.000.000.1241 where is 1241 
is a liability account. Now in distribution line you have 
given the accounting code combination as 02.111.111.1300 
where 1300 is a expenditure account. Now an entry will be 
generated in GL as follows:
02.111.111.1300 Dr.
02.000.000.1241 Cr. That means this option will 
automatically offset the Balancing segment from the default 
segment 01 to 02 in your liability account.
2)If you enbale "Account" the entry will be as follows for 
the above example:
02.111.111.1300 Dr.
02.111.111.1241 Cr. That means this option will 
automatically offset the all other segments alongwith the 
balancing segment in the accounting code combination 
without effecting the account head.
3)If you enable "None" then the accounting entry for the 
above example will be as follows:
02.111.111.1300 Dr.
01.000.000.1241 Cr That means nothing will be offseted at 
any segment in the accounting code combination.Then this 
will be an inter-company transaction.

by quering the table fnd_product_groups and check the value 
of the column multi_org_flag. If the value is 'Y' then 
organization in using multi org features else not.

Functional Specifications document is done based on the 
project we are working.

When ever any one asks about functional specification 
suppose in AP.

What is their Payables calendar?
R there any recurring invoices?
what are the input tax types they are using?
R there any WHT?
Wt is their ship to and bill to locations?
Wt r the different payment terms?
Who r there suppliers?

The questions above are sample.  If u have answers for your 
RD20 questionaire.  BP80 is avaible to describe their 
future process model. 

U have u r Functional specification defined.

The Functional Specification document describes the 
functionalities, processes, event  related to payables it 
is AP and Purchasing if it is PO.

Thnks and Regds
Swathi