It can be very hard to identify good sources, regardless on what it may be. There's no real quick and easy answer on how to learrn more about any given topic, but the only advice I can give is read. I'd honestly stay away from most documentaries and the like, since those are almost always written to entertain first. They can be fun, but they should be a jumping off point for burgeoning interest in a topic, rather than how you learn in and of itself.

Now, of course, there can be issues in deterrmining whether a source is good or bad. None of these are going to be perfect, of course. There are going to be fantastic sources that fall outside the guidelines I give, and there can be horrible sources which fall within in them. Often, the only way you can tell them apart is to engage closely with reputable sources, and recognise aguments being made that rely on rhetorical devices much moe so than the argument. That being said, I can recommend a few general questions to ask when you're trying to determine if the source is reliable:

1. Look up the author. Who are they? Are they someone who has been educated in history, or do they have an education in a different field entirely? What's their experience in? Does it seem like they'd be knowledgeable about this topic? What's their experience in the topic area?

2. Look up discussions of the book. Where is it primarily being discussed? Are there academic reviews of it? What do they say? What about general reactions?

3. Look through the book. Does the author cite sources? Is there a bibliography of works cited? Do major assertions have notes on them, or are they left uncited? If you can, follow up on those citations. Do the sources cited for a particular point actually support the point being made?

These can be a good way to try and judge whether a source could be reliable or not. You can also try perusing the AskHistorians booklist which has a lot of very valuable works that can are generally reliable. This can be a good jumping off point for further research.

On the HRE in particular, I can recommend you try and get a copy of Peter H. Wilson's Heart of Europe. Wilson is a fantastic scholar of the HRE, and this work is probably the best starting point if you're interested in it. It can be quite dense, but, unfortunately, dense reading is going to be par for the course. Hopefully this helps you get your feet on the ground with your journey into learning about history!

Please feel free to ask any follow ups.