Feral is a fun class for me, it avoids everything Rogue had became (Which even before Shadowlands came out).
The covenant choice for Feral druid is in fact Night Fae because they have a absurd burst potential but I think Kyrian is okay too, just check out their abilities and compare.
As for getting the idea, they’re pretty good, if played right, in any situation, raiding, mythic (Single target or AOE). Though they require some very fineness in making sure you don’t run out of resources each time. So starting out and leveling, always go for the most friendly talents that make both AOE, and target to target fighting flowing.
As for stats, always, ALWAYS have crit first (After agility of course) and then Mastery because your passives depend on it for easier resource management and damage overall. Critical hit provides any combo point generation ability two instead of one on crit each time from a passive as you level. Mastery just makes bleeds and finishing moves hurt much more.
As far as Legendaries goes, just check Icy-Veins or WoWhead for that, they’re the same and provide the same answers for any situation but in personal experience, I run Cat-eye-curio because I use so much energy at times and it evens out my overuse of my spending.
If there’s any advice in particular. whether or not in single target or AOE, always have each bleed on your targets, ALWAYS, even Thrash, that adds significantly to shred/swipe damage. And when you have Rip on target, always use ferocious bite from then on (Unless the target is weak, then ferocious bite is generally better.) In AOE, go with Primal Wrath talent for a AOE Rip, and like I stated before, then start using Ferocious Bite and try to keep Rip applied at all times. The most damage I ever gotten in this expansion’s raid and Mythic runs were doing this. Sadly both wowhead and Icy-Vein led me astray on that saying Primal Wrath every time in AOE.
The talents listed on both sites provide clear information for either single target or AOE (go with AOE since most scenarios is gonna be more than one target anyways unless you aim to be really be at the top all the time). So they’re straightforward and easy to choose from.
Overall, Feral is NOT a easy spec to play as, I’ll tell you that much. Even when I started during Cataclysm and eventually past WoD, I finally grasped how to play them and during those bad changes up until Shadowlands, I figured out very comfortably how they play and my only issue is just keeping energy saved for all of my bleeds which is a must to have on your enemies at all times, keep them refreshed and you’ll most likely do a lot of damage among your team. Just practice the rotation of Going into stealth first if possible > rake > Thrash > shred (Singletarget) = Swipe (AOE) > Rip or Primal Wrath for AOE at 5 combo points. then just shred or swipe accordingly and Ferocious Bite but always keep the bleeds up at all times as needed. Their healing is also provided by the combo points accumilated, especially at 5 points which gives you a proc of free self healing, which is powerful when it crits. There is also a issue with it because Wild Growth will throw you out of Cat form but there is a macro that prevents it unless you have a proc ready (You can look that up, I assume).
If this is too much information, just go to WoWhead or Icy-Vein to get your general info and practice in game by then, as you level, you’ll learn and get the feel of how to effectively play them. I may not be the best with Feral Druid and someone may have a MUCH better understanding than I do but I get around well with mine that I don’t feel terrible in comparison to other players I’m against.