For these errors in particular, there is a small guide in the documentation here that touches on the “Accessed None” error as well as gives a few different examples of referencing actors. If you’re more of an audio learner this tutorial is very succinct and quick while still giving pretty insightful information. Keep in mind that both of these relate to your problem but aren’t a direct resolution to it, so it would be more for understanding why you’re getting the errors you are to hopefully help prevent some of them in the future.
@midgunner66 did an absolutely beautiful job of breaking down the concept of this error in particular. These resources will really only expand further on the same points, but it can be helpful seeing a problem tackled from multiple angles and with a few different examples.
As for learning about/from the runtime errors in general; they definitely can and do seem vague, especially whenever it comes to a new system you’re just diving into or have just started experimenting with. The best way to start with any of them is to break down the runtime error section by section and follow along in the blueprint. I’ve also personally found that building my C++ skills has helped exponentially with understanding how to work with blueprints directly as well.