how do i set up chained payments?

I'm trying to set up chained payments. I watched the video, searched the forums and searched google for the answer, however all I found are people who used a document that I can't seem to download and a lot of confusion...

Specifically, I have a paypal account set up. The instructions say "You must login to PayPal and create an API signature to get your credentials. Instructions »" but that link goes to a page with about 50 options and I don't know which to use...