The article below is just a basic introduction to the topic. For something more advanced, written by pros and a fantastic leveling guide, my recommendation would be this Elder Scrolls Online Leveling Guide. I could not find any other guide that comes even close in terms of the impact it had on me.
Guilds in TESO are very similar to how they worked in older Elder Scrolls games. They’re lore-based NPC followings you can choose to join in order to gain access to new quests, new lore, new vendors and new skill lines. You don’t have to choose between the various guilds in TESO. You can join all of them if you wish. You may wish to choose a primary guild or two, however, especially considering that skill points are limited.
There will be four guilds in the game when it first launches: Mages Guild, Fighters Guild, Vampire Guild and Werewolf Guild. The Dark Brotherhood Guild and Thieves Guild will be added post-launch. Mages Guild and Fighters Guild appear very early on in the game’s storyline and you can join either or both by completing a series of introductory quests. You’ll gain access to new skill lines and new vendors immediately.
Guild Skill Lines
The skill lines for both Mages Guild and Fighters Guild are essentially what you’d expect. Fighters Guild skills consist of mostly melee and support active abilities that do extra damage to Undead and Daedric opponents, specifically. The passives support the active abilities and allow players to intimidate NPCs in conversations as well as accept guild-appropriate bounty quests in Cyrodil.
The skill line for the Mages Guild consists of active abilities that will come in very handy for spell casters such as the eso sorcerer. Effects include extra damage-over-time abilities, extra area-of-effect abilities and a buff that reveals invisible opponents while buffing the caster’s damage. The passives increase damage, effect duration and allow players to persuade NPCs in conversations.
Both skill lines also include an Ultimate ability. The Mages Guild Ultimate deals a great deal of AoE damage while providing a knockback. The Fighters Guild Ultimate is a close-range AoE ability that deals additional damage to Undead and Daedric enemies.
For players who choose to join the Vampire and Werewolf guilds for their character progression, the skill lines consist of various active and passive abilities including an ability to temporarily turn into the a Vampire and/or Werewolf. These guilds appear later in the game. There is also an Ultimate ability for each of these guilds. Keep in mind that a player can only have one Ultimate ability slotted per weapon set equipped.
The skill lines for the Dark Brotherhood and Thieves Guild will most likely consist of abilities that are focused on stealth, sneaking, lockpicking and other rogue-like strengths.
The article above is just a basic introduction to the topic. For something more advanced, written by pros and a fantastic leveling guide, my recommendation would be this Elder Scrolls Online Leveling Guide. I could not find any other guide that comes even close in terms of the impact it had on me.