Helpful links I use more or less daily:
Warframe Hub - Lists timers for stuff, active missions, bounties in Cetus, which Alerts are active etc etc. I keep this up on my second screen basically all the time.
Warframe market - A marketplace for players. Make a account and you can post stuff, if you just wanna buy no account needed. With a account you can place BUY ORDERS, this can save you 10-30% of the price. Very easy to use, search for what you need, press a button and you get a copypaste string you just paste inside Warframe with a ready tell to the person selling.
Tenno Zone - Nice "planner" function if you wanna farm for specific drops from relics. Tells you which relics drops stuff, and where to farm the relics most efficient.
Warframe Reddit - Just a forum, and you'll probably be surprised how amazingly friendly this community is. Forget the cesspool that's reddit in other games
Official forums – A personal favourite is the "Players helping Players" forum. I browse it often just to catch questions other are asking, which is usually stuff I wonder about as well. Very informative and helpful.
All Resource best Farm Locations 2018 - Just a forum post, and I can't guarantee it's 100% reliable, but I always check if when I forget where some resource drops.
Weapons required as crafting ingredients - Don't sell some weapon you crafted if it can be used to create something new!
Warframe Wiki - Amazing. Just amazing. Has more or less all the info you can ask for. Active discussions in MOST of the entries as well, so don't forget to scroll down and check what people are talking about regarding what you searched for.
Aaaand self plug if someone wanna start:
Referral Link - Gives you a 7 day XP boost and gives me some unlockable bonuses as people are refered
Know some played it a few years back, but A LOT has changed since. I didn't play it back then, but those who did says it's a whole new game. More or less all systems has been reworked, there's a pretty rich story and just a buttload of content.
I'm about 80 hours in, having a blast. The learning curve can, even though there's a tutorial, be quite steep. First 3-4 sessions I played less than 1 hour each, but then I got completely stuck.
The movement is very parkour-ish, LOTS of dashes, airglides, wall jumps etc. At first it felt very odd, coming from normal shooters, but it grows on you.
There's 30+ "classes"/Warframes, group dynamics, story missions, progression, hundreds of weapons etc and you customize everything with mods that you level up.
You can farm basically everything. Some "delux" warframes/weapons have been retired, but are still available for sale from players. So you farm the newer stuff, sell that to players (for the currency you can buy with RL money) and buy older stuff as well.
TIP: Do NOT start spending cash. It's not needed what so ever. The game is a lot about collecting stuff, getting stronger, collecting better stuff. Well, you get the idea. So if you spend cash, you're kinda buying yourself out of playtime. At least play few days, get the hang of it, THEN chose if you wanna put some money in. I have put like 20€ in so far, for some weapon slots and warframe slots (the only thing I'd recommend spending RL money on at start, if anything).
Also, you get a daily reward that can be a bit of ingame currency, xp boost etc. But you can also get a 50% or if you're lucky 75% discount on the RL-cash currency (called Platinum), so might wanna wait for that if you're going to spend any money.
And if you try it, don't get overwhelmed. There's A LOOOOOOT of content, mechanics and stuff built up over the years. Just pace yourself
Not sure how long it'll last, but since it's F2P there's no harm trying.
Can add me ingame, SinfulSupernova