How do am I suppose to know what is canon and what is not?

I feel like all my knowledge of 30k and 40k lore is both a mix of misunderstood and straight up wrong at any given point. Every time I try and correct myself I am bombarded with people saying "oh this is how it actually is" and then someone else saying "Actually it's like this". I just desperately want to understand how the fucking Waaagh actually works or Is Alpharius actually Omegon pretending to be Alpharius dressed up as Omegon. I know this is due to the ever shifting landscape of retcon, but how do y'all keep the up to date canon straight?