Warframe

I don't know of a good pre-existing newbie guide... so I'll type one up myself:

Top thing is multi-tasking. In warframe it's almost always best to be doing a few things at once since this is a grind-game. So doing more grinds simultaneously or incidentally grinding while doing something else is very good.

As for specific things to do start with filling out the Star Chart and hitting Quests. I'm listing these together because unlocking more of the Star Chart unlocks more quests for you. Do missions until you have a quest, then do the quest (or at least chip away at completing it), then repeat until you're out of Star Chart & Quests.

There's a few things that scale with Mastery Rank (MR), think of it as your account's level, and some weapons are gated behind having some MR level or another. You get MR by leveling up... pretty much everything but only the first time for each piece of gear. So leveling up a spare set of your starting gear doesn't help you here. You'll be given a skills test when you've ranked up enough stuff to reach the next MR, practice the test in a Relay with Cephelon Simaris because some of them are hard and you have to wait a day if you fail outside of practice mode.

Grabbing blueprints off the Market or your Clan Dojo's various Research Labs, building them, and ranking them up is a great way to get most of the MR ranks. This also pairs very well with completing the Star Chart and helps you find what style of weapons you like. After that farming Warframes from the boss fights on each planet is the next best source of MR (and some of the Warframes are legitimately awesome).

Now to address the mechanics you've specifically asked about:

The Railjack is used in The New War (quest) and in the Lich system so I'd recommend putting a little work into yours but you by no means need to master the skill of Railjack use or fully kit it out. Passable skill and OK mods will get you all the further you need.

Archwings are nowadays mostly just used in Railjack missions and for traveling across the Open World areas quickly. Until you get to Steel Path (hard mode) you're really not going to need really any effort put into your Archwing, however Archguns are worth putting effort into because they're used as summonable heavy weapons and the primary weapons for Necramechs.

Void Keys have been retired as a mechanic. You no longer need, or can even acquire, them. You now access the Void through it's connections to Europa, Neptune, and Sedna on the Star Chart. There are however Dragon Keys used to open vaults in Deimos missions... it's worth doing but they keys have nasty debuffs so best to do that with friends/PUGs.

There's a few things made with materials from Fishing and Nightwave will periodically have fishing as one of the weekly tasks so it's worth the minimal effort and moderate time investment. I'd highly recomend grabbing the Oxylus companion from The Business on Fortuna (it helps so much).

Mining... honestly is in the same category as Fishing except you'll want to get mining lazor upgrades from Cephelon Simaris instead of the companion from The Biz.

I thin you're referring to Modular weapons & companions here? Non-modular stuff I've talked about above. Modular stuff is by no means necessary but once your comfortable with non-modular stuff it's worth experimenting with it, making your own Moa/Hound companion, guns tailored to your specific tastes... they're nice.

You mean Operator/Drifter stuff, right? They're wholly unnecessary until you reach the Zariman. They're certainly nice to have and the farming for it is entirely incidental, just slap Lenses on maxed gear that you like and you're off, but you definitely don't need it. Honestly, while the Operator/Drifter is technically needed for some stuff base-level will generally work fine in most situations.

PvP is like 99.99% dead. There's no need to learn it and beyond pure enjoyment of it little reason to do it.

Riven Mods are unnecessary. However they're a great way to give weapons you particularly like a little extra kick. Other than that the Riven market is a nice source of Platinum as unwanted Rivens can be sold to other players for Platinum.

There is a late game that requires you to put in some effort, the Steel Path. You unlock it my entirely completing the Star Chart then talking to Teshin. This gives you access to the Steel Path Star Chart and some nice rewards from working on it. +100 levels on each node, +250% enemy Shields & Armor. It's fun but it can get frustrating with some mission types.