Links to the different TERA Discord Servers
Here's a collection of direct links to the various TERA related discord servers. They vary from class specific discords to stuff like the NA publisher discord and reference and related topic discords.
You'll often read that the discord servers are the best source for information but honestly, some of them can be pretty troll and unhelpful. Your mileage will vary depending on who's on and what you are asking. Most of the class servers will have channels set up to keep gearing and other character setup related information easily accessible. Sometimes it's in text form, sometimes in graphical form, and sometimes it'll be a link to the off-server guide.
Wait, what the heck is discord
Just in case you didn't already know, discord is an all-in-one voice and text chat for gamers. You can check out their site here, and the discord server links below will also get you to their site.
But I don't want to use discord...
If you don't want to use discords, there are related guide pages in progress that are static versions of the content from the discords and their linked guides. Discord is really okay, and you can even run it in a browser if you don't want to have the app. Give it a try at some point. Just don't feed the trolls.
En Masse Entertainment
From the welcome-rules channel "Welcome to the Official En Masse Entertainment Discord!" Has categories for TERA PC. #terapc-news is mostly (entirely?) the TERA twitter feed. The TERA PC subsection has all the TERA related channels. Complain about the game in #terapc-general, try to find a group in #terapc-lfg, chuckle at the name sellers in #terapc-trading, and try to be helpful to the people asking questionsin #terapc-support. The support channel is actually pretty helpful since regular users will offer help as well as staff.
Tera Discord Hub
From the info channel "This discord is meant to act as hub between all public TERA discords. Main purposes is to link all "listable" discords, as currently each individual discord links to some random subset of them."
Notable discords not listed here but listed in the hub are the #regional-discords, #console-discords, #pvp-discords, #tool-discords.
Tera Server Status
Useful for catching when the servers go down and come back up for both planned and unplanned reasons. You can use this as a quick alert for server status changes by muting all the channels except for #notifications.
The Lancer class discord. An open discord (no verification required) with channels for character setup as well as a bot for quick info.
The Brawler class discord. Dunno why but it took me forever to realize it's a fist icon XD. When you first join, you get access to the #guides and #faq-and-gear-and-glyphs channels. To get full access, you'll need to verify your player status by posting a picture of your in-game character profile and what region / server tag you want to have.
The Warrior class discord. An open discord minus one channel that requires self-role assignment to access. Decent memes as well though really, every class discord that has a memes channel will end up seeing every other discord's memes eventually.
The Berserker class discord. Don't zerk much but seems like this is the place to be for berserkers. From the info, it sounds like there was a berserker discord prior to this one that closed or isn't available anymore. Berserker also has a google site similar to the Valkyrie guide site.
The Gunner class discord. You can access all the information channels regularly but chatting requires that you verify with a picture of your gunner profile window and what region tags you want. This is one of those discords that can be kinda trolly and unproductive for help but it's all we've got. There's also a gunner implementation of the Prav.js bot to do moongourd log analysis, comparing your his per minute and uptimes versus the script's recommended values. Invoke it in the #moongourd channel with !senpai pls moongourdlogurl. Add your character name after the URL if there was more than one gunner.
The Archer class discord. A comparatively "small" (few channels) class discord, you only need to self assign a role for chat permissions in the discussion channels. Archer is the only class that keeps an updated essential mana page.
The Slayer class discord. Info is broken out into channels. Self-assign a region role if you want to chat. The info channels are great.
The Slayer class discord. Open discord as far as I can tell, self assign roles but doesn't look like it locks out chat if you don't. The guide is in the channel text...
The Valkyrie class discord. General info is available on joining the server but additional information is available after you self-assign a region and platform role. The guide is available on a google site but is out of date. Current info is embedded in the chat... which kind of makes it hard to access.
Tera Ninja Discord
The Ninja class discord. Posted guide info is a bit outdated but you can probably get current info from the chat if you try hard enough.
The Sorcerer class discord. This one is the smaller one. I dunno if it's up to date since I don't play Sorc much.
The other Sorcerer class discord. This one is the larger one. Seems like there's a good amount of info here and it's organized into well named channels. The "guide" is embedded in the channels.
[TERA] Priest & Mystic
The Priest and Mystic classes discord. I heard someone tease that this is more of a fishing discord server. Dunno, I barely play healer. Channels are organized into categories for Priest and Healer with a lot of additional useful game info for game optimization and mod usage. "Guides" are embedded in the channels.