History classes and arguing with people on the internet, mostly. Unfortunately productive arguments are much harder to come by online now. It's really useful to hear explanations of why you're wrong about something that introduce information or ideas you haven't considered before, even if you still aren't going to agree it challenges you to update your position to convincingly explain why you're still right despite that stuff. The problem is that so much of what's out there focuses on persuasive rhetorical strategies and much less on any kind of meaningful substance regarding what is actually true and how the world works, because in the end hardly anyone actually cares about or values that or has time for it. At least there's still books though. Find books by people who have spent years seriously engaging with and researching the thing they are writing about and read them.

If you're feeling confusion and uncertainty, I think that means you're on the right track, hold on to that uncertainty.