How is "PayPal" different from "Visa" or "MasterCard", in facilitating E-commerce?

Suppose I want to buy from (or sell to) someone overseas.

They don't accept Visa, they don't have a Merchant account.

Maybe they have a Bank Account but they don't want to disclose it or the massive Bank fees for Transferring a small amount of Money (as well as the prevailing Exchange Rate moves about all the time) from my $AUD NAB to their € BNP account makes the entire Transaction unviable.

PayPal cuts through this and allows me to transfer funds from my PayPal $AUD to their Paypal € and PayPal handle the transfer at the prevailing rate for a smaller fee.

PayPal also offers specific Safety and protection policies

To mention the obvious paypal is easier, faster and secure. Its easier to input your paypal username and password rather than the numbers on the card, Its secure since the merchant never gets your card info. But the main reason behind making paypal successful is the fact that you can create a dispute to recieve a refund and the paypal team will investigate giving buyers and sellers a sense of security

Paypal gives buyer the security because its a tool created Ebay. Ebay if you dont already know is a buying and selling website or e-commerce in simpler words. When you end up buying something which did not meet its specification, you can create a dispute and get your money refunded. 

I have personally disputed twice, and won both time. One of the dispute was on the late shipment. I paid extra $25 for24-48 hours shipment, but i recieved the item in72 hours. I disputed and sent the reciept to paypal and they helped me get a refund on my extra shipping cost. There is no way Mastercard or visa is going to let you do that.

Rapidity, ease of use, and most importantly, security.

i am user of paypal,,,its fine it pays on your behalf with out showing your card , bank account etc,, 

paypal is online payment method account connected with your credit card bank , you can pay through the paypal on alot of online shopping website , the paypal account gives you security and safe payments that is done by the same credit card account without  entering the card details on the website,