Am I understanding casting right that
it allows you to get the information
from other blueprints to use in
another blueprint
That’s true enough, but that isn’t exactly what casting is.
Casting is more like converting, or re-interpreting, an object reference as a more specific object type. For example, let’s say you have a APawn reference that is passed through a function as its more general type, AActor. In this state, you could only do AActor-related things with this reference. If you needed to do Pawn-specific actions on it instead, you’d first have to cast it from its more general type (AActor) to the specific type, APawn. But remember, you can do this only because APawn derives from AActor. By contrast, you could not cast an APawn reference into, say, a UWidgetComponent, because neither of those types derive from each other.
So, in other words, casting is like saying, “I have an object reference that I know can be converted into a more specific type, so please give me back a reference in the form of the more specific type so I can do specific stuff with it.”
In your case, assuming your “BoxTest” blueprint is deriving from the ATriggerBox class, you’d be able to cast a ATriggerBox reference into a BoxTest reference and then access the custom variables and functions you’ve created in your BoxTest blueprint.
Hope that helps clear things up a bit.