Best places to start are:
^ That's the late Pat Rogers' final lecture, which provides an excellent foundation to build upon. He's an excellent lecturer, so grab a light snack and something to wash it down with - the hour goes by quite fast.
From there, currently, I would say that The School of the American Rifle website/blog, YouTube Channel, and Facebook Group would be a great place to start your initial dive into the pool. https://www.schooloftheamericanrifle.com
, and https://www.facebook.com/SchooloftheAmericanRifle/
This resource will get you thinking along the right lines.
As you start understanding that there's more to lowers than "a lower is just a lower" and start seeing a larger section of the sky than just what's outside your window, you'll want to prep a meal (or two) and plop down in front of your monitor/tablet/phone for this sit-in party:
^ This is a monster of a P&S (Primary & Secondary) Modcast and really starts the deep-dive. It is a great compliment to the in-depth information that you start to see (and sometimes try to climb out of!) with the SOTAR stuff that I listed above.
If you really like doing homework and are willing to do a bit of digging, the M4Carbine.net and P&S Forums both have a much higher signal-to-noise ratio than AR15.com, and are immense resources for the platform. For starters, I'd join M4Carbine.net if you haven't, and once there, start searching for the membername Iraqgunz
. That's the screen-name of the late Will Larson, the man behind Semper Paratus Arms (old FB page here: https://www.facebook.com/SemperParatusArms/
- it's also chocked-full of excellent information; I'd also encourage you to simply Google search for the terms "youtube semper paratus arms"), who passed away last summer. His open-enrollment armorer's courses were a staple of the hobbyist community and professionals alike, and his old posts on M4C contain so
much wisdom and experience to siphon off.
The ARBuildJunkie website is also a good place to get some background information. I haven't been on their Forums, but their interviews, Buyer's Guides, and How-Tos all seem to be on-point.
Finally, consider signing up for an AR-specific training class. Typically, beginner/novice classes of even the "run your gun" (aka "weapon manipulation") type will feature at least a morning's worth of fundamental mechanical knowledge that can often contain more than what the average hobbyist/owner knows. Even moreso, there are now more and more open-enrollment "armorer's classes" specific to the AR15 platform: anything from a multi-day class that gets into the real nitty-gritty to just a single-day's quickie that hits much more in-depth than just a basic breakdown/knowledge (like what's typically found in the morning/first-day sessions of the weapon manipulations classes) can make you so much more knowledgeable - helping you not only better maintain your weapon, but also giving you the knowledge and skills necessary to do everything from effecting *proper* upgrades/modifications and remediation of existing problems all the way to helping you become a better operator of the system (as understanding the mechanics of the gun's inner workings will help you better diagnose stoppages on-the-fly, while shooting).
Years ago, I attended a one-day "armorer's course" designed for hobbyist owners/shooters, hosted by Weyer Tactical here in NE-Ohio. The class was taught by Dave Laubert (of Defensive Creations), who is a member of the American Pistolsmith's Guild. Although an "informal" class, each student still got to tear down their ARs all the way down to individual components and then rebuilding from the ground up, remediating any problems and/or making upgrades/updates along the way while also pointing out to us what each part should be (in a not-over-the-top, let's gauge everything manner, but rather, in a more relaxed, "hobbyist" manner), and why it should be what it should be. At the end of the class, he brought out a slide show that was compiled during his years with Pat Rogers (much of the AR folks in my area are disciples of Pat or, like me, have been taught in-turn by those disciples) which documented numerous stoppages and failures - from the commonplace to the rare/unique - and discussed with us what the cause(s) was/were, and how to remediate for each. I can't even begin to express how much I learned from those 8 hours in the classroom, and ever since then, I'd wanted to take a multi-day, true-armorer-level course (I'll likely hit up SOTAR next calendar year).
Hope this helps!