Before registering a real PayPal account, I strongly recommend you to try the PayPal Sandbox first.
With PayPal Sandbox, you can create both buyer and seller accounts to simulate the whole PayPal ransaction process. It also allows you to test the Instant Payment Notification and the Payment Data Transfer which you may implement in your web application. This makes sure the whole payment work flow could be tested completely before it runs on the production server.
Registering a PayPal Sandbox account is completely free and it is independent with your real PayPal account.
Visit PayPal Sandbox
Reference: PayPal Sandbox User Guide (PDF)