You are not aware of the PayPal payment gateway and you need to integrate PayPal in your PHP website then this tutorial will help you with how to integrate PayPal in the PHP website. No need to work with the hard code just simply follow the below steps and you can get the PayPal workable in your PHP website.
Click Here for download the PayPal standard code for PHP.
If you need to work with the live account then set the below URL in your form action
If you need to work with the sandbox account then set the below URL in your form action
Now you need to set your paypal email to the business input fields.
Also set the notify url, return url and cancel url of your website. where page will redirect after the action call.
When you follow the above steps successfully then you can get the paypal working in your php website.