The first thing that you will need to do in order to use Direct Blueprint Communication is to identify the Blueprints that will be communicating.
Above we have a Character Blueprint and a Ceiling Light Blueprint which we want the character to be able to turn off.
In this instance, the working Blueprint is our Character Blueprint and we are targeting the Ceiling Light Blueprint. Through Direct Blueprint Communication we can say that when the player character presses a button, target the Ceiling Light Blueprint and turn off the light. To do this we would need to create a publicly exposed variable inside our character Blueprint, targeting a Ceiling Light Blueprint.
Above inside our Character Blueprint we have created a variable of the Blueprint Ceiling Light type and we've also set it to Editable which will allow us to set the instance of the light we want to affect in our level.
Be careful about which variables, functions, and events you expose. Do not expose variables unless it is safe for other people to access and change them. As a best-practice guideline, expose only what other Blueprints need and what you want level designers to be able to change, as opposed to exposing everything.
In our level with our Character Blueprint selected, we can see the new variable that we can then set from the Details panel.
Click image for full size.
By default the variable is set to None and must be set to define which instance of the ceiling light you want to affect, as you could have multiple ceiling lights in your level and you need to define which one you want to communicate with. You can click the drop-down menu (or eye-dropper icon) to select from the level and specify which instance you want to communicate with.
Since we only have one ceiling light in our level, only one is shown however if we had more they would be listed in the drop-down.
Once you define which instance you are going to directly communicate with, you will then be able to access that light's functionality, variables or other settings from inside your Character Blueprint.