You are not aware of the PayPal payment gateway, and you need to integrate PayPal into your PHP website; then this tutorial will help you with how to integrate PayPal into the PHP website. No need to work with the hard code; just simply follow the below steps, and you can get PayPal working in your PHP website.
Step 1)
Click Here for download the PayPal standard code for PHP.
Step 2)
If you need to work with the live account, then set the below URL in your form action.
https://www.paypal.com
If you need to work with the sandbox account, then set the below URL in your form action.
https://www.sandbox.paypal.com/cgi-bin/webscr

Step 3)
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 the page will redirect after the action call.
Step 4)
When you follow the above steps successfully, then you can get PayPal working in your PHP website.