payment-processing

Am having a lot of trouble getting my head around this paypal payment stuff... How can i confirm that the user has successfully signed up for my subscription? I know 0 about IPN but for example : If a user signs up to my website with example@e.com but uses the paypal account sample@s.com to pay then how to i match up the user. I read that PDT do not send out a transaction ID (tx) for recurring (subscription) payments is that true ? Just need help with it all... honest and easy :) Thanks. Yeah sometimes is hard to understand Paypal and all their documentation but for any kind of subscription i

We know there are so many payment gateway service providers namely paypal, moneybrookers, authorize.net and many national and international payment gateway providers. Now, my question is what are the steps to develop our own payment gateway service to process any visa and mastercard regardless of any bank of the world. From which organization should i need to take authority to develop my own payment gateway service. What are the api and protocols provided by www.visa.com and www.mastercard.com to develop own payment gateway service. I don't know that payment gateway service provider's api has