The first thing you need to do is to login to the PayPal developer website: http://developer.paypal.com
Use your existing PayPal username and password to login. Once logged in you’ll arrive at the Dashboard. Navigate to Applications → Sandbox accounts
Now we’ll need to create 2 test accounts – 1 for the merchant (representing your shop’s PayPal account) and 1 for a buyer (representing a customer).
On your website:
Select checkbox: Enable PayPal standard
Use the merchant test account email you created above for the PayPal & Receiver email
Select checkbox: Enable PayPal sandbox