Skill Lines in ESO- what are they and why might you want to start leveling them

PVE

Mages Guild
Fighters Guild
Undaunted
Psijic Guild
Vampire
Werewolf
Thieves Guild
Dark Brotherhood
Legerdemain
Scrying & Excavation
Scribing

PVP

Assault
Support

Crafting

Alchemy
Blacksmithing
Clothing
Enchanting
Jewelry Crafting
Provisioning
Woodworking

Crafting, Mages, Fighters, Undaunted and PVP skill lines were mentioned in the Introductory Guide so I’ll refer you to that document and not repeat that information here.

Werewolf and Vampire skill lines can be acquired at “shrines” in the game and have mechanics, buffs and debuffs associated with them which I suggest you look into dedicated guides online for more information. With the Werewolf rework in U50, wolves are now meta for endgame content. Vampirism can be useful in some situations/game play styles.

Dark Brotherhood is a guild which is oriented toward the thief/assassin style of play. Again, read about it in a dedicated guide if that play style interests you.

The Legerdemain skill line is useful for primarily one reason (for non-thieves). When maximized, you can “force” chest locks without having to “pick” them. Otherwise this is again a skill line oriented toward thief/assassin players.

The Psijic Guild is a quest line in Summerset which opens a skill line with some niche useful skills. If you find yourself needing these skills; head to Summerset and do the quests there.

Scrying and Excavation are the skills needed to “Scry for Leads” that you’ll get as drops in the game. The leads when excavated will give you household items, but most importantly will yield items which combine to form very useful gear items that are “meta” for endgame content. (eg, Huntsman’s War Mask, Velothi Ur Amulet, Oakensoul Ring, etc) This is a multipart quest line that starts with Adept Irnard Rirnil outside any Mage’s Guild or via the “Collections>Collectibles>Update” menu. Once completed on one character, subsequent characters only need to finish the first “wing if the indrik” quest to obtain the skill line. Scribing Skill allows you to modify other Skills and customize them for your needs.