credit card are that card from which we can purchase any
goods and services on the behalf on payer(bank), the bank or
lending company pay the amount, after the specific time
limit (differ by credit limit) we have to pay the money to
bank if we fails to pay the money then interest will charge.
debit card are those card from which we can incurred any
expenditure the amount deduct one's banks accounts.

A debit card permits you to pay from your account where as 
by using a credit card you are actually borrowing from the 
issuer of such a credit card promising him to pay at a 
later date. Depending up on the terms and conditions and on 
teh nature of transaction you either pay interest to teh 
lendor or enjoy a interest free credit period. There is no 
interest in case of debit card as there is no borrowings.

Note: Usually some merchants collect an additional 2% when 
you pay by card. you can insist non payment of taht 2% if 
you are paying by debitcard. 

FUNDA: This 2% the merchant collects from us is nothing but 
the interest collected by bank for teh free credit period - 
only that it is collected from the merchant.