I am new to VM, I just learn that i must had to install plugin in order to accespt credit card in my VM2
So is there any free plugin availalbe which i can use?
There are several payment plugins already installed in VM, each requiring you to have an account with a payment processing service. Whichever you use depends on where you are located and which services are available in your country. If you already have a business bank acount with a merchant card processing service then it makes sense to use them if possible. Most small sites start off using something simple like PayPal, but their card processing service is not available in every country, as in some they require a PayPal account for both seller and customer.
If a suitable payment plugin in not already included in VM then there are more available, check our third party forum section or http://extensions.virtuemart.net/payments (and also the JED).
Can you name any free one (if possible default) one using which I can accept credit card?
As I said, it depends on your country - but in the UK PayPal offers credit and debit card handling, free to set up. There is no free option just to obtain credit card details.