DEBIT THE RECEIVER AND CREDIT THE GIVER( Perosnal account) 
DEBIT ALL EXPENSES AND LOSS AND CREDIT ALL INCOME AND GIANS
( Nominal accoutns)
DEBIT WHAT COMES IN AND CREDTI WHAT GOES OUT (Real 
accoutns) 

BANK EARN INCOME THORUGH INTEREST ON MONEY LENDING AND 
OTHER SERVICE CHARGES

There is a 3 golden rules of accounting as follows.
1] Personal Account 2] Real Account 3] Nominal Account
The bank wiill give the loans to customers on interest and 
earn profit.

Every Debit has a correspondent Credit vice versa.
By Interest on loans.

The main function of banks are accepting deposits from
public and lending the same. The difference in rate of
interest for acquiring deposit and lending loan is called as
"spread" and the same is the main source of income for
banks. Bank also getting income by agency function like
collecting chq, follwing standard instruction and other
utility functions.

Golden rule : 
1. Receivable are Debit and Payable Are Credit
2. All the expeces and loss are " Debit " and ALl the 
profit and income are treat " Credit".
3. All the assets are debit and all the Liablities are 
credit.

Bank gives a lone and advance to the customer and get a 
interest and profit. and any other charge create by the 
banker . those are point to souece to earn.

All the bank gives the loan to the customer and it's 
turnover is fixed. When the customer did not pay his 
instalment they charged interest. interest is their profit.

Answer for - "Golden Rules of Accounting?"

Golden Rules of Accounting:
   There are totally 3 kinds of Accounts in Financial 
Accountancy. They are
1. Personal Account - relates to name of the person, 
organization, institution etc.
2. Real Account - relates to cash, assets.
3. Nominal Account - relates to incomes, expenditures, 
losses and gains(profits).
   These three kinds of accounts contains 2 rules each, 
which are as follows.
1. Personal Account:
   Debit "the Receiver"
   Credit "the giver"
2. Real Account
   Debit "what comes in"
   Credit "what goes out"
3. Nominal Account
   Debit "all expenses and losses"
   Credit "all incomes and gains"
    These are the three Golden Rules of Accounting.

Answer for "How Bank Earn Profit?"

   Bank earn profits from the interest rates collecting 
from various types of loans. i.e., Bank offers less rate of 
interest on deposits and makes high rate of interest on 
loans and through this bank earn profit.