i never do payment gateway on projects so need help to integrate payment-gate-way. is there any one to help me?
There are a bunch of resources. Just one thing I want to throw out. Think about PCI DSS compliance.
You do not want to have even a single credit card touching your server for even a fraction of a second (irrespective of whether you store it or not). if you do, the site is within scope for PCI DSS and for a small project the administrative requirements are very burdensome (read the detailed instructions, not just the bullet points you need to cover - it’s a huge PiTA).
If the client doesn’t care about branding, Paypal is an easy option or you could do something like authorize.net SIM (NOT AIM). If they do, check out Braintree Payment Systems.
I’d avoid Paypal Payflow Pro (used to be Verisign Payflow Pro) or Authorize.net Advanced Integration Method as both will mean card data is transmitted by your website, putting it within scope for PCI DSS.
Once you’ve chosen a provider, ask again on the list (or just google for a gem) - there’s lots of very easy to use information available.