Help in PayPal PHP Algorithm

I want write a PHP registry code That when a User regi开发者_JS百科stried than go to PayPal site and give some money to us and after her payment , her account activation in our site Automatically . what am i going to do ? Thanks in Advance .

Check out Paypal's Payflow Link : https://cms.paypal.com/us/cgi-bin/?&cmd=_render-content&content_ID=developer/howto_gateway_payflow_link

The user on your website clicks the Paypal buy button, gets transferred to Paypal to do their payment, and then returns to your website (wherever you specify) to finish.

Look into Paypal's IPN functionality.

Here is the link to Paypal's IPN PHP API setup that they provide. There should be plenty of snippets / tutorials available from Google though.

EDIT

Also a great resource is http://developer.paypal.com it gives you access to a sandbox to setup test accounts with money etc to test the functionality of your newly implemented system before you send it live.