Which step is it?
I honestly do not remember. It seems to be incomplete and / or offers more than one method of approach. It was more of a proof-of-concept rather then ready-to-go solution. These are usually more involved than what’s shown.
edit: all the necessary pieces to make it work are above. But, obviously, I don’t know what you’re doing, how you’re choosing the materials and what you’re applying them to. Everyone has different needs.
It’s an Event Dispatcher. It does not contain anything per se. It’s a method of communication between blueprints. Widget dispatches (talks) and the actor registers (listens to) it. It connects those two entities together.
How to set it up depends on you, the material selection can happen in the widget or in the actor. Both approaches will work fine. If the widget also needs to displays the material (like a product configurator), it probably makes more sense to contain the material selection logic within the widget.
Again, it all depends on the desired end result.
Perhaps you could start a new thread and describe what is needed. Do include details and your progress so someone can offer a solution that fits into your current setup.