Funds are transferred electronically from the customers bank account to yours. (This is a highly simplified explanation, and is accurate in the most general sort of way. However, the bottom line is that the customer buys, and at some point the funds are removed from his or her account and ultimately deposited into yours.)
The best known method is the issuing of electronic checks Customers pay for merchandise by writing an electronic check that is transmitted by email, fax or phone. The "check" is a message that contains all of the information that is found on an ordinary check, but it is signed digitally, or indorsed.
The digital signature is encoded by encrypting with the customer’s secret key. Upon receipt, the merchant or "payee" may further indorse by encoding with a private key. When the cheque is processed, the resulting message is encoded with the bank’s secret key, thus providing proof of payment.