For the best result, you should hire experienced developers. Bcoz, they can develop and integrate suitable payment module with your website. According to me, PayPal, Authroize.Net, and First Data are the excellent payment gateways which offer secure payment transaction services.
A payment gateway facilitates the transfer of information between a payment portal (such as a website, mobile phone) and the Front End Processor or acquiring bank. Here is a step by step guide detailing how Payment Gateways work:
When a customer places an order on website by pressing “SUBMIT ORDER” and enter card details.
If the order is via a website the customer's web browser encrypts the information to be sent b/w the browser and the merchant's webserver. This process is done by SSL(Secure Socket Layer) encryption.
After that merchant forwards transaction details to their payment gateway. This is also another SSL Encrypted connection.
*The payment gateway forwards transaction info. To the payment processor used by the merchant's acquiring bank.
*The payment processor forwards the transaction info to the card association(like VISA, MASTERCARD etc).