paypal e-commerce documentation

I'm looking for a module that - or some method - that has a User/client pay for a subscription at login.
In other words, if one wants to subscribe to the Journal/Magazine, then you are asked to pay via PayPal, and upon success returned to the appropriate Magazine page.

For example. I have Moodle installed on my site, and it has this function to allow access to courses.
To use the site - other than look at the front page, a user registers, leaving their email address. Ok, that's normal.

I'm just wondering if there are any actual instructions or docs for using eC3 with Paypal? For instance, in the eC setup page for paypal, it says the payment processing page is 'https://www.paypal.com/xclick/' -- is that correct, up-to-date info? Because I can't find it anywhere else.

The successful payment url shows "%order-history' -- is that a correct setting? And the Paypal IPN request-back validation url, set to 'http://www.paypal.com/cgi-bin/webscr' -- is that correct? I can't any of this stuff documented anywhere, and it's about as clear as mud, what it all means.