The term BlueprintImplementableEvent is a bit misleading I think. It basically acts as a specifier to allow for blueprint overrides of functions. So in your case you can have a blueprint that gives the function “Event” a body that is executed whenever the function is called.
The equivalent of actual Events in C++ is called Delegates. You can find the documentation for them here:
If you create multicast delegates and mark them BlueprintAssignable you can also use them from blueprints.
greetings
FTC