Hi Indranil
General Ledger is the main Ledger where all accounts are maintained. Vendor and Customer ledgers are sub-ledgers where each line item transaction is kept vendor/customer wise.
In general ledger one Reconciliation/Dy Debtor/Sy creditor account is opened and maintained in Vendor/Customer Master. This account is the link between General Ledger and Sub-Ledger of Vendor and customer.
When any invoice is posted against any vendor/customer system goes to Master data of that vendor/customer and find out the Recon account defined in the vendor/customer Master and link the transaction with that to post it to General Ledger.
I think you have got your answer.
kamal