add payment method in shop backend settings

Have you read the documentation? This should get you what you're looking for.

thanks for your reply, i have already read the documentation. kentico shop already support paypal,authorize.net, like this i have prepared and developed new custom payment gateway in shop frontend. Now, i have to create form in shop backend for saving merchant details like paypal(client id,account type,etc,).what is the procedure to create a form in shopbackend. i am waiting for your reply.

The documentation has all the information you need to be able to create the form as well. If you need further inspiration on creating the form, look at the Authorize.NET form located in the file system here:

\CMSModules\ECommerce\Controls\PaymentGateways\AuthorizeNetForm.ascx

i am already create the form in front end payment page.this documentation have the information only for creating the form in checkout payment page.now i need to create the form in shop admin page.

I am using paypal in my ecommerce website , this is one of the finest payment gateway i have ever used.