Addons in ESO are a way to customize your UI and help players get more information without leaving the game. You can get most by visiting esoui.com and installing them manually or by instslling the minion client that will do it for you. Here are some I recommend.
Wykkyd Gaming suite – gives a lot of UI tweaks with information including inventory space, research times, time, quests, resource bar adjustments, dialogue numbering, and more. you even get options to get less UI and more immersion options.
Srendarr – a buff and debuff tracker, let’s you know when to reapply something.
Awesome Guild Store – helps search and filter guild store results MUCH easier and also shows you the price per unit on item stacks.
Circonians FilterIt – help search and filter your inventory.
Shyshards – shows all sky shards on a nap. I recommend this AFTER you’ve played and explored a bit and are working on Alts.
Lost treasure – gives a red X where a treasure map or survey will take you, when in your inventory. use this only when you’very been searching a zone for hours.
Lorebooks – Use this when you’ve search a zone and haven’t found all the books. but fo take time to search for them yourself.