Blueprints Communication

In UE4 a new feature is that actors can be built in self-contained blueprints with their own set of internal variables, functions and events. That's fine, but how does one blueprint get variables from another blueprint?

This puzzled me, so I looked up UE4 Answer Hub and patched together what I wanted from Zak Parrish's example. He was printing a string of variable values from one blueprint via a function in another. I wanted a score to be dynamically updated each time an actor in the scene was touched by the player, and not just use a fixed increment value, and I wanted the score to draw continually on the HUD. So how?

I made a 30 minute explanation video. It really took me a few days to get my head around the process I have to say. I tried out a lot of different things, and was really close for most of the time, but a couple of necessary steps hadn't occurred to me. Now I've figured it out, and I feel less hobbled by the newness of UE4.

A lot of crashes occurred during the recording and editing of the video clip, so you can imagine my nerves. But I'm super happy to finish it up.