i d like t know too lol, i hear it often too, but it looks like its very complex topic and long one.
It's just that u shouldnt take a certain action, because u r always taking it only with AA/KK so then maybe it can be better to just not do it , i.e. like 5betting deep PF with AA only, so then lets say u would be 1000bb deep and he can play perfectly vs. u preflop(call for setmine odds)/postflop since he knows wut u hold.. so its better to just call4b /AA PF etc...
then i think fundamentals are also about having strong understanding of mathematics in poker, to know when u overfold, overbluff ... when u can bet / raise with ATC and have autoprofit with given sizing etc
but i rly am not right person to talk about this, i play now 10nl only and played highest only 25nl deep with mega shitty 15BI BRM..

+1 It would be cool to have an essential video series to poker fundamentals. Most theory is assuming we already have this. But it's pbb not really easy to make.

I think a sort of 'pareto princple' in poker would be cool. The 20% most important stuff that makes up most of your results.

Let me just brainstorm on what I'd consider fundamentals...
- equities, both preflop and post, understanding that AA is 82% vs KK-22, QQ is 47% vs JJ+,AK, etc, etc, having an idea about the equity of the NFD vs top pair, etc, etc.
- calculating pot odds
- calculating implied odds
- calculating fold equity
- calculating EV of semi-bluffs
- combinatorics (i.e. AKo = 12 combos, QQ = 6 combos, AQ+,TT = 62 combos and knowing what that means in your HUD, so 62 combos = 4.68%, understanding what a 15% opening range looks like, etc, etc.

I'm not sure whether I'd include any GTO stuff in the fundamentals. I think that's a bit beyond. Feel free to add to the list, it's just something I came up off the top of my head.

As far as RIO doing a video, I think I disagree. There's a lot of articles all over the web covering this stuff, it's covered in almost every book aimed at beginners, etc. I haven't checked but I'd imagine there's some decent links in the FAQs over in the Micro and SS forums at 2+2.