The linked article provides very little info on how it actually works. What's the point in writing about something, if you are not going to say anything meaningful?

I just interviewed with Venmo and although they declined to offer, I want to say that they were some of the brightest and most focused people I've had the pleasure of meeting. We discussed Touch a bit in the several rounds of interviews and all the members were clearly excited about it and loved to discuss technical details and design decisions that went into making Touch.

So congrats, Venmo team!

There's a walkthrough of how it works along with screenshots at https://touch.venmo.com/

The previous title on this HN post was more informative without context on what Venmo or Touch is: "Braintree Launches Venmo Touch: One Touch Payment Across Apps"