If you do not know about Paypal Gateway, you can read this manual to learn about it. Paypal Overview Paypal Developer Documentation There you need to create two accounts (Business (Seller) & Personal (Buyer)), I have already created these accounts. If you also created PayPal accounts, then install PayPal.
After that, click on the settings button.
Here you need to write your Paypal Business account and select the sandbox payment mode (test mode) or “Live”, and in the latter case, copy this IPN URL and put it into your PayPal Business account, After that, just click on the Save button
Now you have set up your PayPal gateway on your side. There you have to put your IPN URL.